Electrolyte delivery and generation equipment

ABSTRACT

An apparatus for automatically generating a metal-containing electrolyte (e.g., an electrolyte containing Sn2+ ions and an acid) includes an anolyte chamber configured to house an active anode (e.g., a metallic tin anode), an anolyte, and a sensor (e.g., one or more sensors) measuring a concentration of metal ions in the anolyte; a catholyte chamber configured to house a hydrogen-generating cathode and a catholyte; and a controller having program instructions for processing data from the sensor and for automatically generating an electrolyte having metal ions in a target concentration range in the anolyte chamber. In some embodiments, the apparatus is in communication with an electroplating apparatus and is capable to deliver the generated electrolyte to the electroplating apparatus on demand. In some embodiments, a densitometer and a conductivity meter are together used as sensors, and the apparatus is configured to generate low alpha tin electrolyte containing an acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/921,602 filed Oct. 23, 2015 titled “Electrolyte Delivery andGeneration Equipment”, naming Mayer et al. as inventors, which claimsbenefit under 35 U.S.C. § 119(e) to U.S. Provisional Patent ApplicationNo. 62/168,198, filed May 29, 2015, which are herein incorporated byreference in their entirety.

FIELD OF THE INVENTION

This invention pertains to an apparatus and method for generatingelectroplating liquid (electrolyte) for electroplating metals onsemiconductor substrates in a semiconductor fabrication facility. In oneimplementation this invention pertains to an apparatus and method forgenerating Sn²⁺-containing electrolyte from tin metal.

BACKGROUND

Tin is a metal that is often used in fabrication of semiconductordevices (e.g., in solder bumps). Tin and its alloys (e.g., tin-silver)can be deposited by electrodeposition on a partially fabricatedsemiconductor device using an electrolyte containing Sn²⁺ ions, and,typically, an acid. Tin, however, is often contaminated with elementsthat emit alpha particles that are detrimental to the function ofsemiconductor devices. Specifically, alpha particles are known to causeso-called “soft errors” in data storage devices. Therefore, a specialgrade and type of tin electrolyte, an electrolyte that contains very lowamount of alpha particle emitters, should be used for electroplating tinin semiconductor devices. This electrolyte is referred to as low alphatin electrolyte. The specification for “low alpha tin”, as used herein,refers to tin having an alpha emission rate of less than 0.002 counts(alpha disintegrations) per hour per square centimeter. The alphaemission rate is typically measured from a metallic tin layer that hasbeen plated from low alpha tin electrolyte. While such electrolyte iscommercially available, it is extremely expensive. Tin metal (referringto tin in zero oxidation state) is also available in low alpha tin form,purified from a mixture of various alpha emitting isotopes and aged toensure that residual radioactive isotopes have followed their decaypaths and have finished their fission processes. The metallic low alphatin is significantly less expensive than low alpha tin electrolyte. Thehigh cost of low alpha tin electrolyte is due to the significant cost ofmanufacturing, certification, packaging and shipping from the place oforigin to the place of use of the acidic hazardous liquid electrolyte,which is added to the moderately high cost of low alpha tin raw materialthat is used to manufacture the electrolyte. Commercial low alpha tinmetal is 4 to 20 times less expensive than the tin in the electrolyteproduct, on a metal content basis, after shipping costs are taken intoaccount.

SUMMARY

A method and an apparatus for generating electrolyte from a metal (inzero oxidation state) directly in the semiconductor fabrication facilityare provided. The method and the apparatus can be used to generateelectrolytes containing a variety of metal ions, including tin, nickel,and copper ions from tin, nickel and copper metals respectively. Tin,and particularly low alpha tin electrolyte, is generated by theapparatus in many illustrative embodiments, but the invention is not solimited.

There is a substantial economic advantage in producing the electrolyte“on-site” in the semiconductor fabrication facility. Furthermore, whenthe electrolyte is manufactured on-site, in some embodiments, the sametool that manufactures the electrolyte is also configured to deliver thegenerated electrolyte to the electroplating tool. This design ischaracterized by an advantageously efficient use of equipment, materialsand space, as well as by reduced on-site labor costs and by improvedoperator safety, since the need to pour electrolyte from barrels to theelectroplating baths is minimized or eliminated. In some embodiments,the on-site automated electrolyte manufacturing and delivery apparatusis designed to communicate with the electroplating tool (e.g., SABRE 3D™electroplating tool, available from Lam Research Corp. of Fremont,Calif.) to respond to operator and process-protocol requests foradditional electrolyte.

In one aspect, an apparatus for generating an electrolyte containingmetal ions is provided. In one embodiment the apparatus includes: (a) ananolyte chamber configured to contain an active anode and an anolyte,wherein the apparatus is configured to electrochemically dissolve theactive anode into the anolyte; (b) a first catholyte chamber separatedfrom the anolyte chamber by a first anion permeable membrane, whereinthe first catholyte chamber is configured to contain a first catholyte;and (c) a second catholyte chamber configured to contain a cathode and asecond catholyte, wherein the second catholyte chamber is separated fromthe first catholyte chamber by a second anion permeable membrane. Theanolyte chamber includes an inlet for receiving a fluid; an outlet forremoving the anolyte; and one or more sensors configured for measuring aconcentration of metal ions in the anolyte. In some embodiments theactive anode is a low alpha tin anode, and the apparatus is configuredto generate low alpha tin electrolyte as the anolyte in the anolytechamber.

In some implementations, the first catholyte chamber and the secondcatholyte chamber are parts of a removable cathode-housing assembly,wherein the removable cathode-housing assembly is configured to bereleasably inserted into the anolyte chamber.

In some embodiments the apparatus is configured to deliver the firstcatholyte from the first catholyte chamber to the anolyte chamberthrough a fluidic conduit, e.g., a fluidic line and/or to remove thefirst catholyte from the first catholyte chamber to a drain. It is notedthat ion-permeable membranes, as used herein, are not classified asfluidic conduits (although a small amount of fluid may be transferredthrough the membrane along with the ions).

In some embodiments the first catholyte chamber and the second catholytechamber are fluidically connected through a fluidic conduit, wherein thefluidic conduit allows for transfer of the second catholyte from thesecond catholyte chamber to the first catholyte chamber.

In some embodiments the apparatus includes a single piece metal anode inthe anolyte chamber. In other embodiments the anode is composed of aplurality of metal pieces and the anolyte chamber includes anion-permeable container for containing these metal pieces thatcollectively form the anode. In those embodiments, where the anode isformed by a plurality of metal pieces, the anolyte chamber may furtherinclude a receiving port for receiving the plurality of metal piecesinto the ion-permeable container. In some embodiments the receiving portincludes a gravity fed hopper and may further be equipped with a sensorconfigured to communicate to a system controller when the level of metalpieces in the port is low.

The provided apparatus typically includes a hydrogen-generating cathodepositioned in the second catholyte chamber. The apparatus may include adiluent gas conduit configured to deliver a diluent gas to a space abovethe second catholyte, and to dilute hydrogen gas accumulating in thatspace, wherein the space above the second catholyte is covered with afirst lid having one or more openings that allow for transfer of dilutedhydrogen gas into a space above the first lid. In some embodiments theapparatus further includes: a second lid over the first lid and spacedapart from the first lid such that there is a space between the firstand the second lids; and a second diluent gas conduit configured todeliver a diluent gas to a space between the first and second lids andto move the diluted hydrogen gas from the space between the first andsecond lids towards an exhaust.

In some implementations of the provided apparatus the anolyte chambercomprises a cooling system. In some embodiments the cooling system islocated in a cooling portion of the anolyte chamber away from the anode.In these embodiments the apparatus may further include a fluidic conduitand an associated pump configured to deliver the anolyte from theanolyte chamber outlet located proximate the anode to the coolingportion of the anolyte chamber.

In some embodiments the apparatus is configured to measure theconcentration of metal ions in the anolyte with one or more sensors, andto communicate the measurement to the apparatus controller. In someembodiments the one or more sensors include at least two sensors: adensitometer, and a conductivity meter which allow for accuratedetermination of metal ion concentration in the presence of acid, whereacid concentration may fluctuate. In some embodiments one or moresensors (e.g., a combination of a densitometer and a conductivity meter)are also configured for measuring the amount of acid in the anolyte. Insome embodiments the preferred conductivity meter is an inductive probe.

In some implementations the apparatus includes a controller havingprogram instructions for automatically generating electrolyte having aconcentration of metal ions in a target range.

In some embodiments the apparatus further includes a storage containerin fluidic communication with the anolyte chamber and with anelectroplating cell, wherein the apparatus is configured for automatedtransfer of the anolyte from the anolyte chamber to the storagecontainer, and from the storage container to the electroplating cell.

In some embodiments the apparatus further includes a buffer tank influidic communication with the anolyte chamber, and with a replaceabletote, wherein the buffer tank is configured to receive an acid solutionfrom the replaceable tote and to deliver the acid to the anolytechamber. In some embodiments the apparatus is further configured foridentifying the low level of acid in the replaceable tote and forproviding a signal for tote replacement.

In another aspect, an apparatus for automatically generating anelectrolyte containing metal ions, is provided, wherein the apparatusincludes: (a) an anolyte chamber configured to contain an active anodeand an anolyte, wherein the apparatus is configured to electrochemicallydissolve the active anode into the anolyte, and to thereby form theelectrolyte containing metal ions, wherein the anolyte chambercomprises: (i) an inlet for receiving a fluid; (ii) an outlet forremoving the anolyte; and (iii) one or more sensors configured formeasuring a concentration of metal ions in the anolyte; (b) a catholytechamber configured to contain a cathode and a catholyte, wherein thecatholyte chamber is separated from the anolyte chamber by an anionpermeable membrane; and (c) a controller having program instructions forautomatically generating an electrolyte having a concentration of metalions in the anolyte chamber in a target range using data provided by theone or more sensors.

In another aspect a system is provided, wherein the system includes: (a)an electroplating apparatus that utilizes an electrolyte containingmetal ions; (b) an electrolyte-generating apparatus configured forautomatic generation of the electrolyte, wherein theelectrolyte-generating apparatus is in communication with theelectroplating apparatus; and (c) one or more system controllerscomprising program instructions for communicating demand for electrolytefrom the electroplating apparatus to the electrolyte-generatingapparatus and for generating electrolyte having concentration of metalions in a target range.

In another aspect, a method of generating an electrolyte containingmetal ions is provided, wherein the method includes: (a) passing currentthrough an electrolyte-generating apparatus, wherein the apparatuscomprises: (i) an anolyte chamber containing an active metal anode andan anolyte; and (ii) a catholyte chamber containing a cathode and acatholyte, wherein the catholyte chamber is separated from the anolytechamber by an anion-permeable membrane, wherein the anode iselectrochemically dissolved into the anolyte as current is passed; (b)measuring concentration of metal ions in the anolyte, and automaticallycommunicating the concentration to an apparatus controller, wherein theapparatus controller comprises program instructions for processing thedata on concentration of metal ions and for automatically instructingthe apparatus to act based on these data; and (c) automaticallytransferring a portion of the anolyte from the anolyte chamber to anelectrolyte storage container, when concentration of metal ions in theanolyte falls within a target range.

In some embodiments the concentration of metal ions in the anolyte ismeasured by a combination of a densitometer and a conductivity meter. Insome embodiments the anode comprises low alpha tin metal and the anolytecomprises Sn²⁺ ions. In some embodiments the anolyte further comprisesacid, and the method further comprises measuring concentration of acidin the anolyte; automatically communicating concentration of acid to theapparatus controller, wherein the apparatus controller comprises programinstructions for processing the data on acid concentration and forinstructing the apparatus to act based on these data. For example, themethod may involve automatically adding acid to the anolyte if theconcentration of acid is less than a target concentration range.

In some embodiments the method further comprises dosing the anolyte withan acidic solution, after a portion of the anolyte has been transferredto the storage container, and repeating operations (a)-(c). In someembodiments no more than 10% of the total volume of anolyte istransferred from the anolyte chamber per one (a)-(c) cycle. In someembodiments, the method involves performing at least three (a)-(c)cycles with addition of acid to anolyte after each cycle. In someembodiments the anolyte and catholyte comprise an acid selected from thegroup consisting of methansulfonic acid (MSA), sulfuric acid, andmixtures thereof.

According to another implementation, a non-transitory computermachine-readable medium is provided, wherein the medium includes programinstructions for control of an electrolyte generating apparatus. Theinstructions include code for electrolyte generation methods providedherein, and may further include instructions for storage of generatedelectrolyte in a storage tank and delivery of the electrolyte to anelectroplating apparatus.

In some embodiments systems and methods provided herein are integratedwith photolithographic patterning processes. In one aspect, a system isprovided, wherein the system includes an electrolyte generatingapparatus provided herein and a stepper. The system typically furtherincludes an electroplating apparatus in association with the electrolytegenerating apparatus. In some embodiments, a method is provided, whereinthe method includes generating electrolyte as described herein andfurther includes electroplating metal on a semiconductor substrate usingthe generated electrolyte. In some embodiments the method furtherincludes: applying photoresist to the wafer substrate; exposing thephotoresist to light; patterning the photoresist and transferring thepattern to the wafer substrate; and selectively removing the photoresistfrom the wafer substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic presentation of a system having an electrolytegenerating apparatus in communication with an electroplating apparatusaccording to an embodiment presented herein.

FIG. 1B is a schematic isometric view of a modular system having anelectrolyte generating apparatus according to an embodiment providedherein.

FIG. 2 is a schematic cross-sectional view of an electrolyte generatingapparatus according to an embodiment provided herein.

FIG. 3A is a schematic cross-sectional presentation of an electrolytegenerating apparatus according to an embodiment provided herein, wherethe presentation illustrates a configuration of fluidic connections.

FIG. 3B is a schematic cross-sectional presentation of an electrolytegenerating apparatus according to an embodiment provided herein, wherethe presentation illustrates another configuration of fluidicconnections.

FIG. 4 is a schematic cross-sectional presentation of an electrolytegenerating apparatus according to an embodiment provided herein, wherethe presentation illustrates a configuration of sensors in theapparatus, according to an embodiment provided herein.

FIG. 5 is a schematic cross-sectional presentation of a catholytechamber having a two lid hydrogen management system according to anembodiment provided herein.

FIG. 6A is a side view of an electrolyte-generating apparatus accordingto an embodiment presented herein.

FIG. 6B is a side view of the electrolyte-generating apparatus shown inFIG. 6A illustrating the opposite side of the apparatus.

FIG. 6C is a cross-sectional view of the electrolyte-generatingapparatus.

FIG. 6D is another cross-sectional view of the electrolyte-generatingapparatus.

FIG. 6E is a perspective view of the electrolyte-generating apparatus

FIG. 6F is an isometric view of a removable cathode-housing assemblyaccording to an embodiment provided herein.

FIG. 6G is a cross-sectional view of the removable cathode-housingassembly.

FIG. 6H is another view of the removable cathode-housing assembly.

FIG. 6I is a close-up view illustrating the inner lid in thecathode-housing assembly.

FIG. 7A is a side view of a portion of an electrolyte-generatingapparatus according to an embodiment presented herein, where theinterface between the anolyte and catholyte chamber is illustrated.

FIG. 7B is another side view of a portion of an electrolyte-generatingapparatus according to an embodiment presented herein, where theinterface between the anolyte and catholyte chamber is illustrated.

FIG. 7C is a cross-sectional view of the electrolyte-generatingapparatus according to an embodiment provided herein.

FIG. 8A is a process flow diagram for a method of generating electrolyteaccording to an embodiment provided herein.

FIG. 8B is a process flow diagram for a method of generating electrolyteaccording to an embodiment provided herein.

FIG. 9A is a first portion of a diagram illustrating anolyte andcatholyte compositions during electrolyte generation according to anembodiment provided herein.

FIG. 9B is a continuation of a diagram provided in FIG. 9A.

FIG. 9C is a first portion of a diagram illustrating anolyte andcatholyte compositions during segmented acid electrolyte generationaccording to an embodiment provided herein.

FIG. 9D is a continuation of a diagram provided in FIG. 9C.

FIG. 9E is a first portion of a diagram illustrating anolyte andcatholyte compositions during electrolyte generation according toanother embodiment provided herein.

FIG. 9F is a continuation of a diagram provided in FIG. 9E.

FIG. 10 is an experimental plot illustrating correction of anolytedensity drift in accordance with an embodiment provided herein.

FIGS. 11A-11D are process flow diagrams illustrating adjustments to theprocess in response to measurements provided by sensors.

FIGS. 12A-12B are experimental plots illustrating linear dependence ofsolution density on tin ion concentration.

FIGS. 12C-12D are experimental plots illustrating linear dependence ofsolution conductivity on acid concentration.

DETAILED DESCRIPTION

An apparatus for generating an electrolyte for an electroplatingapparatus is provided. The apparatus is configured to generate anelectrolyte having a desired concentration of metal ions, and, in someembodiments, a desired concentration of acid. The apparatus isillustrated using generation of an acidic low alpha tin electrolyte froma low alpha tin anode as an example, but it is understood that theapparatus can be used to generate a variety of electrolytes, such as anelectrolyte containing nickel ions from a nickel anode, an electrolytecontaining copper ions from a copper anode, etc. The apparatus can alsobe used to generate non-acidic electrolytes, such as electrolytes havinga pH of greater than 7 (e.g., basic electrolytes containing complexingagents).

In some embodiments the apparatus is capable of generating anelectrolyte with a concentration of metal ions that fluctuates by nomore than about 15%, such as by no more than about 10% (e.g., by no morethan 7%) of the desired concentration in the output electrolyte. Forexample, if the desired concentration of tin ions in the electrolyte is300 g/L, the apparatus is capable of generating an electrolyte havingtin concentration within the range of 255-345 g/L, such as within therange of 270-330 g/L, more preferably within the range of 280-320 g/L.The range of concentrations that are acceptable for a given purpose isreferred herein as a target concentration range and as a “broad targetconcentration range”. For example, the electroplating apparatus mayrequire a stock of tin electrolyte with a desired tin ion concentrationof 300 g/L and with acceptable fluctuation of concentration of no morethan 7%. In this case the electroplating apparatus is configured togenerate an electrolyte with the broad target concentration range of tinions (Sn²⁺) of between about 280-320 g/L.

In some embodiments, the electrolyte generating apparatus is alsocapable of generating electrolyte having a stable concentration of acid(e.g., sulfuric acid, an alkylsulphonic acid, such as MSA, and mixturesthereof). The range of acid concentrations that is acceptable for agiven purpose is referred to herein as a target acid concentration rangeor a “broad target acid concentration range”. In some embodiments, theconcentration of acid in the electrolyte product fluctuates by no morethan 25%, such as by no more than 20% of the desired acid concentration.For example, in some embodiments, the electroplating solution shouldhave a target MSA concentration of 45 g/L with a fluctuation of no morethan 10 g/L. The electrolyte generator, in this case, will generate theelectrolyte with a broad target concentration range of acid of betweenabout 35-55 g/L. In some embodiments the fluctuation of MSAconcentration in the electrolyte product should be no more than 5 g/L,such that the concentration of MSA is within a broad targetconcentration range of between about 40-50 g/L.

In addition to the term “broad target concentration range”, the term“narrow target concentration range” will be used herein to indicate aconcentration range of an electrolyte component, which is sufficientlyclose to the desired concentration, such that no correction ofelectrolyte generation process parameters is required. For example if abroad target concentration range for tin ions is 280-320 g/L and anarrow target concentration range is between about 290-310 g/L, anelectrolyte product with tin ion concentration of 300 g/L (within bothbroad and narrow ranges) would not trigger any corrective action for theapparatus, but an electrolyte product with a tin ion concentration of315 g/L (within broad range, but outside the narrow range), wouldindicate that the generated electrolyte is acceptable as a product, buta corrective action should be taken in subsequent electrolyte generationto lower the tin ion concentration to the narrow target range.

The terms “broad target range” and “narrow target range” apply not onlyto concentrations themselves, but also to electrolyte properties thatcorrelate with concentrations of electrolyte components, such asdensity, conductivity, and optical density. The meaning of these termsis similar to those described above. Thus “broad target range” indicatesthat this range is acceptable and does not require process shut-down,while “narrow target range” indicates that this range is not onlyacceptable at the time of measurement, but also does not raise any redflags that would trigger process parameter adjustment for generation ofa future batch. For example if the broad target density range forgenerated product is between about 1.48-1.52 g/cm³, it means that anelectrolyte with a density falling outside of this range is notacceptable as a product. If the narrow target density range is betweenabout 1.49-1.51 g/cm³, it means that an electrolyte with a densityfalling outside of this range but within the broad target range would beacceptable as a product, but that the apparatus will need to take acorrective action and modify electrolyte generation process parameters,in order to bring the density in future batches of electrolyte to thenarrow target density range.

In some embodiments, the generation of electrolyte is partially orcompletely automated. Automation, as used herein, refers to execution ofprocess steps (such as addition of one or more chemical componentsand/or removal of the produced electrolyte) with reduced or eliminatedmanual labor. For example one or more of the following examples ofautomation can be used, in one apparatus. In some embodiments, one ormore physicochemical properties of the electrolyte being manufacturedare automatically measured by one or more sensors and these are used todetermine the concentration of metal ions in the electrolyte (i.e. theelectrolyte properties are automatically measured) as the electrolyte isbeing generated, and these data are electronically communicated to theprocess controller, where the process controller has programinstructions for removing the electrolyte to the storage container oncea target concentration of metal ions has been reached, and/or fordiluting the electrolyte if the concentration exceeds the targetconcentration range. In some embodiments the controller is programmed toremove a portion of the electrolyte to a storage container, after apre-determined amount of charge has passed through the apparatus,wherein the pre-determined amount of charge is the amount of charge thatis necessary to bring the metal ion concentration in the electrolyteinto the broad target range. The calculation of the required charge ismade based on Faraday's law. The controller may also be programmed toprocess data from a sensor measuring metal concentration in theelectrolyte (including any property correlating with the metalconcentration), before the electrolyte is transferred to the storagecontainer. The controller can allow the transfer if the concentrationfalls within the broad target range, and disallow the transfer, if theconcentration falls outside of the broad target range. The controllermay also be programmed to modify process parameters for futureelectrolyte generation, if the measured metal concentration fallsoutside of the narrow target range, while still being within the broadtarget range.

In some embodiments, the concentration of acid is automatically measuredby one or more sensors during generation of electrolyte, and these dataare communicated to a controller that has program instructions forautomatically adding more acid if the concentration of acid isinsufficient, or for automatically diluting the electrolyte with waterif the concentration of acid is too high.

It is understood that the “concentration measurement” by a sensor canrefer to the measurement of any property that correlates with theconcentration. For example, the concentration measurement of tin ionscan be performed by measuring the density of the electrolyte (providedthe concentration of acid is known), while measurement of acidconcentration can be performed by measuring the conductivity of theelectrolyte (provided the concentration of tin ions is known). In someembodiments it is preferable to measure both the conductivity anddensity of the electrolyte (e.g., anolyte), since both of theseparameters positively correlate with metal ion concentration and acidconcentration. Therefore, if both density and conductivity are measured,the combined data can be used to accurately determine both metal ionconcentration and acid concentration in the electrolyte. In someembodiments, where the concentration of acid is known to be relativelystable during the electrolyte generation process, only densitymeasurement of electrolyte may be sufficient to accurately gauge theconcentration of metal ions in the electrolyte solution. In someembodiments, particularly where acid concentration in the electrolyte isrelatively low, the density of electrolyte will most strongly depend onmetal ion concentration, and density measurement can be used toapproximately measure the concentration of metal ions, whileconductivity may not be necessary to be measured, or may be measuredless frequently than density. In one of preferred embodiments, bothdensity and conductivity of an acidic tin electrolyte are measured todetermine both tin concentration in the anolyte, and acid concentrationin the anolyte.

The measurement of electrolyte properties “during electrolytegeneration” or “as the electrolyte is generated”, does not imply thatthat the electrolyte properties are measured necessarily only whencurrent is applied to the electrodes of the electrolyte generator, asthe measurements can be taken both during application of current, andafter the current has stopped (e.g., when the generation processincludes cycles having “current-on” and “current-off” periods).

Another example of automation is an automated replenishment of anodematerial. In some embodiments, a metal in the form of pellets isautomatically added to an anode container, where automation is achievedusing a gravity fed hopper: as anodic metal is dissolved duringelectrolyte generation, additional pellets from the hopper fall undergravity into the anode container to fill the space freed by thedissolved pellets. In addition, a sensor may automatically measure thelevel of pellets in the hopper and may send a signal to an operator whenreplenishment of the hopper is needed, or if the amount of added pelletsis too large. In some embodiments, the only steps that are performedmanually during electrolyte generation are periodic (e.g. once a week)addition of metal pellets to the gravity fed hopper, and an exchange ofan acid-carrying container (tote) that provides acid solution for theelectrolyte generating apparatus for a full container.

In one aspect, a system is provided, wherein the system includes anelectroplating apparatus that utilizes an electrolyte containing metalions and an electrolyte-generating apparatus configured for automaticgeneration of the electrolyte, wherein the electrolyte-generatingapparatus is in communication with the electroplating apparatus. Thecommunication may be fluidic, signaling, or both fluidic and signaling.When the electroplating apparatus and the electrolyte generatingapparatus are in fluidic communication, the system includes fluidicfeatures (such as electrolyte delivery lines, electrolyte storagecontainer, valves, pumps, etc.) that are configured to deliver theelectrolyte produced in the electrolyte generator to the electroplatingapparatus. When there is a fluidic communication between theelectrolyte-generating apparatus, and the electroplating apparatus thereis no need to manually carry and pour the electrolyte into the containerof the electroplating tool, as the metered (pre-determined) amount ofelectrolyte having known concentration, is provided and delivered by theelectrolyte-generating apparatus. When there is a signalingcommunication between the electroplating apparatus and theelectrolyte-generating apparatus, the electroplating apparatus isconfigured to signal to the electrolyte-generating apparatus whenelectrolyte is needed. For example the system may include a systemcontroller (which may include one or multiple controllers) havingprogram instructions for communicating demand for electrolyte from theelectroplating apparatus to the electrolyte generating apparatus, andfor generating an electrolyte having a target concentration of metalions. In some embodiments, a single system controller can be configuredto communicate with both the electroplating apparatus and theelectrolyte generating apparatus using an electrical or wirelesscommunication, and provide all instructions for operation of both toolsand for their communication with each other. In an alternativeembodiment, each tool (the electroplating apparatus and theelectrolyte-generating apparatus) has its own controller having programinstructions for operating each tool respectively, where the controllerof one of the tools (e.g., the controller of the electroplating tool) isconfigured to communicate with the other tool (e.g., the electrolytegeneration and delivery tool) and is configured to request action fromthe other tool. For example the controller of the electroplating toolcan be configured to demand delivery of electrolyte from theelectrolyte-generating tool and may include instructions for turning ona pump and opening a delivery valve to allow generated electrolyte toflow from the electrolyte-generating tool into the requestingelectroplating tool and its associated electroplating bath. The amountof the delivered electrolyte “dose” can be regulated by an additionalintermediary system controller, the dose-receiving electroplating tool'scontroller, or the delivering electrolyte-generating tool's controller.

The provided methods and apparatus can be used to generate low alpha tinelectrolyte for use in a variety of electroplating apparatuses, such asin apparatuses with an inert (dimensionally stable) anode, and inapparatuses, containing an active low alpha tin anode. The providedelectrolyte can be used as the main electrolyte when the inert anode isused, or as an additional electrolyte for a make-up stream, or otheradditional streams if an active tin anode is used. Examples ofelectroplating apparatuses that use an active anode are provided in theUS Patent Application Publication No. 2012/0138471 filed on Nov. 28,2011 by Mayer et al. titled “ELECTROPLATING APPARATUS AND PROCESS FORWAFER LEVEL PACKAGING” and in the US Patent Application Publication No.2013/0334052 filed on May 24, 2013 by Lee Peng Chua et al. titled“PROTECTING ANODES FROM PASSIVATION IN ALLOY PLATING SYSTEMS”, which areherein incorporated by reference in their entireties.

The electrolyte-generating equipment provided herein, in one embodiment,is configured to interface with a SABRE 3D™ apparatus available from LamResearch Corp. of Fremont, Calif., and is configured to deliverelectroplating electrolyte on demand to the electroplating apparatus indesired quantities and with desired composition (with desired componentsand concentrations). It is understood that the electrolyte deliveredfrom the electrolyte-generating apparatus to the electroplating tool maybe modified before it enters the electroplating cell, e.g., viadilution, concentration, mixing with an acid or with electroplatingadditives (such as accelerators, levelers, wetting agents, carriers andsuppressors), or it may enter the electroplating cell withoutmodification.

A schematic presentation of an example of an automated system forgenerating, storing and delivering electrolyte to an electroplatingapparatus is shown in FIG. 1A. In the depicted example, the systemincludes an electrolyte generating apparatus 101, connected to thesource of metal pellets 103, a source of acid 105 (e.g., a concentratedaqueous solution of an acid in a container, such as an aqueous solutionof methanesulfonic acid, sulfuric acid, sulfamic acid, and combinationsthereof), and a source of water 107. The electrolyte-generatingapparatus 101 has an outlet that is fluidically connected to anelectrolyte storage container 109, which in turn is fluidicallyconnected to three electroplating apparatuses 113, 115, and 117 to whichthe electrolyte is delivered on demand from the electrolyte storagecontainer 109. The electrolyte is configured to be delivered to platingbaths of the electroplating tools 113, 115, and 117 independently, inthe amount that is demanded by each tool. The system provided in thedepicted embodiment contains two system controllers: the controller 119of the electrolyte-generating apparatus, and the controller 120 of theelectroplating tools 113, 115, 117 (in other embodiments eachelectroplating tool has its own controller). The controller 119 is insignaling communication (e.g., electrically and/or wirelessly) with allof the components of the electrolyte-generating tool, and includesprogram instructions for automatically delivering acid and water to theelectrolyte generating apparatus from the sources of water and acid, andfor removing the electrolyte to the storage container 109 when targetconcentration of metal ions is achieved. The controller 120 is insignaling communication with the controller 119, and is programmed tocommunicate the demand from the electroplating tools 113, 115, and 117,and to deliver the electrolyte from the storage container 109 to thebaths of the electroplating tools 113, 115, and 117 based on the demand.

The electrolyte generating apparatus provided herein can be integratedinto a modular system for use in a semiconductor fabrication facility.FIG. 1B illustrates an example of an arrangement of system components ina modular design. In this example, tin electrolyte is generated in thetin electrolyte-generating apparatus 121 that is housed in the tingenerator compartment 123. The tin generator compartment 123 furtherhouses an electrolyte storage tank 125, which receives the electrolyteproduct from the electrolyte-generating apparatus 121. The generatedelectrolyte is pumped out of the electrolyte generator 121, is passedthrough a filter housed in the tin generator compartment 123 and isdirected to the storage tank 125 through one of a plurality of fluidicconnections 127. The electrolyte is stored in the storage container, andis directed to an electroplating apparatus (not shown) through a fluidicconduit when the electroplating apparatus requests electrolyte. Adjacentto tin generator compartment 123, is an acid storage compartment 129,which is configured to house a removable container with a concentratedsolution of acid (e.g., MSA) that may be optionally connected to an acidbuffer container. The role of the acid buffer container is to provide anuninterrupted source of acid during the time when the removablecontainer (an acid tote) is being replaced or is being replenished withacid. In some embodiments the acid tote is housed in the acid totedrawer of the acid storage compartment 129. The acid buffer containerand the removable acid container are fluidically connected to theelectrolyte-generating apparatus 121 through one of the plurality of thefluidic conduits 127, and the apparatus is configured to deliver definedamounts of acid solution to the electrolyte-generating apparatus ondemand. Furthermore, in some embodiments the same source of acid (thebuffer acid container and/or a removable acid container) from the acidstorage compartment 129 is fluidically connected to an electroplatingapparatus (not shown), and the apparatus is configured to deliverdefined amounts of acidic solution to the electroplating apparatus ondemand. In other embodiments, the electroplating apparatus may use aseparate source of acid that is not shared with theelectrolyte-generating apparatus.

The compartment 131 is configured to house a source of a differentelectroplating liquid, a source of a different acid than in acid storagecompartment 129, or an electroplating additive source. In variousembodiments this electroplating liquid may contain ions of copper,nickel, indium, iron, tin (from a different source or at a differentconcentration than in 125), cobalt or mixtures of any of these ions. Insome embodiments the electroplating liquid housed in this compartment isan acidic solution of a salt of any of the metals listed above. Thesource of this different electrolyte may be a removable container (atote) and/or a buffer container holding the pre-manufactured electrolytethat is fluidically connected to an electroplating apparatus. In someembodiments the tote with this different electrolyte is housed in a totedrawer 133 within the compartment 131, where the tote is fluidicallyconnected to an electrolyte buffer tank, that is also housed in 131. Theapparatus is configured to deliver defined amounts of this electrolyteto an electroplating apparatus upon request. In addition to compartment131, the illustrated modular system includes a compartment 132, which isconfigured to house a source of a different electroplating liquid, asource of a different acid than in acid storage compartment 129, or anelectroplating additive source, where the chemistry housed incompartment 132 is different from the chemistry housed in compartment131. The compartment 132 is organized similarly to compartment 131 andincludes a drawer 134 configured to house a removable tote containingthe provided electroplating solution, acid or an additive. The removabletote may be fluidically connected to a buffer tank, which is fluidicallyconnected to an electroplating apparatus. Thus, in illustratedconfiguration compartments 131 and 132 serve as sources of differentelectroplating chemistries for an electroplating tool.

The modular configuration illustrated herein allows the operator tocompactly house the generated tin electrolyte, a pre-manufactureddifferent type of electrolyte, and an acid source in a plurality ofcompartments. In addition, the provided system may include compartment135, which is a drawer that is configured to house a removable container(a tote) and to fill this tote with the electrolyte generated by theelectrolyte-generating apparatus 121. The apparatus is configured toallow one to draw electrolyte from the tin electrolyte storage tank 125and move it into an empty tote housed in the drawer 135. For example, 20liters of tin electrolyte can be drawn from the tin electrolyte storagetank into an empty tote placed in station 135 in order to provideadditional storage capacity, or for a manual delivery of electrolytefrom tin electrolyte filled tote to a plating tool that is not connectedto the tin electrolyte generator 121.

In some embodiments, the presence of an acid buffer tank fluidicallydisposed between the electrolyte generator and a removable acid toteallows for uninterrupted automated supply of acid to the electrolytegenerator. In some embodiments the apparatus is configured to determinewhen the level of acid in the removable acid tote is low, or tootherwise detect that the acid in the tote is used, and to provide asignal for replacing the acid tote with a filled tote. The acid buffertank is configured to receive acid from the acid tote and to deliver theacid to the electrolyte generator (anolyte and/or catholyte chamber),and is typically configured such that it does not run out of acid duringelectrolyte generation.

The system further includes a controller, such as a program logiccontroller (PLC), which has program instructions for performingelectrolyte generation and delivery, monitoring the equipment forvarious errors, and interlock safety. The controller is electricallyconnected with an output display 137 (e.g., a touchscreen display),which allows the operator to monitor operation of the system, and toprovide commands to the controller, when needed. The system is connectedwith facilities 139, which provide sources of deionized water, and inertand/or diluent gases (nitrogen and compressed dry air) that can be usedduring operation of the system. Liquid cooling water (LCW) is alsosupplied as a means of generator heat removal via the internal heatexchange coils. Alternatively, cool circulating fluid may be supplied bya liquid cooling water recirculating refrigeration unit.

Several embodiments of the electrolyte generating apparatus will beillustrated. In one embodiment the electrolyte generating apparatusincludes an anolyte chamber configured to contain an active anode and ananolyte, where the apparatus is configured to electrochemically dissolvethe active anode into the anolyte, and to thereby form the electrolytecontaining metal ions. In other words, the active anode contains a metalthat is electrochemically oxidized to form metal ions in the anolyte,according to reaction (1), where M is metal, e⁻ is an electron, and n isthe number of electrons removed from the metal in oxidation

M→M^(n+)ne⁻  (1)

When the active anode is a tin anode, the tin is electrochemicallyoxidized to form tin (II) ions, according to reaction (2).

Sn→Sn²⁺ +2e⁻  (2)

When low alpha tin is used as the tin anode, the anode material containsonly small amounts of alpha emitting impurities and the resultingelectrochemical dissolution of low alpha tin metal forms low alpha tinelectrolyte that has low concentration of alpha particle emitters, asdesired.

The anolyte chamber has an inlet for receiving one or more fluids, anoutlet for removing the anolyte and at least one sensor configured formeasuring concentration of metal ions in the anolyte. Examples of fluidsthat can be introduced through the inlet into the anolyte chamberinclude water, a concentrated aqueous solution of an acid, a more diluteaqueous solution of an acid, an electrolyte containing acid and a metalsalt, and combinations thereof. The apparatus typically includes one ormore pumps configured for delivering one or more of these fluids intothe anolyte chamber. The outlet in the anolyte chamber serves forremoval of portions of anolyte (where the portions may have variablesizes) from the anolyte chamber. A pump is typically used to remove theanolyte from the anolyte chamber. For example, a portion of the anolytecan be pumped out of the anolyte chamber through the anolyte chamberoutlet, when the concentration of metal ions in the anolyte reaches atarget concentration range. In some embodiments the anolyte chamber isfurther equipped with a cleaning and draining system, which allows theanolyte to be recirculated and filtered during recirculation. The samesystem may be adapted to remove a portion of the anolyte to a drain,when needed. In one example of anolyte recirculation, a portion of theanolyte is removed from the anolyte chamber through the outlet in theanolyte chamber, passed through a filter to remove particles, and isreturned to the anolyte chamber after filtration.

In some embodiments, the anolyte chamber may include more than onesensor. For example, a set of sensors configured for measuring theconcentration of acid and metal ions in the anolyte can be included. Anexample of such set of sensors is a combination of a densitometer and aconductivity meter. The sensors configured for measuring theconcentrations of metal ions and acid concentration generally canmeasure any set of properties of the anolyte that can be correlated withmetal ion and acid concentrations. For example, when tin electrolyte isgenerated, the sensor for measuring tin ion concentration can be adensitometer that measures the density of anolyte. When the densitometeris used in combination with a conductivity meter, both tin ionconcentration and acid concentration can be accurately determined.

If the concentration of acid in the anolyte is relatively low and/or isknown to have only small fluctuations, a densitometer alone can be usedto measure tin ion concentrations. This is due to the strong correlationof anolyte density alone with the concentration of heavy metal (e.g.tin) ions and due to relatively weak dependence of density on acidconcentration. An experimental plot, showing dependence of density onmetal ion concentration at various fixed concentrations of acid showsrelatively weak dependence of density on acid concentration, as can beseen in FIG. 12A. When conductivity is measured in addition to densityin the same solution, a more accurate determination of metal ionconcentration can be made using a plot showing dependence ofconductivity on metal ion concentration at various fixed concentrationsof acid. When the electrolyte generator is used to generate electrolytehaving spectrophotometrically active ions (such as copper or nickelions), the sensor measuring metal ion concentration may be aspectrophotometer which allows for measurement of the metal ionconcentration in even more facile way than measurement of tin ionconcentration through the use of density. In the case ofspectrophotometrically active ions, one can accurately determineconcentrations of metal ions in anolyte using plots of opticalabsorbance dependence on metal ion concentrations. Further, data onconductivity for various metal ion concentrations and acidconcentration, can be used to determine the concentration of acid.

The electrolyte generating apparatus further includes a catholytechamber configured to contain a cathode and a catholyte, wherein thecatholyte chamber is separated from the anolyte chamber by an anionpermeable membrane. This separation may be direct or indirect. Forexample, when the separation is direct, the cathode-housing chamber andthe anode-housing chamber are directly adjacent to each other and thereis a membrane between these two chambers. When the separation isindirect, there may be one or more additional chambers, between theanode-housing chamber and the cathode-housing chamber. These chambersare typically also separated from each other by anion-permeablemembranes.

The catholyte chamber preferably contains an inert, hydrogen-generatingcatalytic cathode. Examples of such cathodes include titanium orstainless steel cathodes coated with platinum or with iridium oxide,where the coating catalyzes the cathodic reaction. Such coatings areprovided, for example, by Optimum Anode Technologies of Camarillo,Calif. A cathodic reaction is shown in equation (3).

2H⁺+2e⁻→H₂   (3)

The separation membrane allows the anions to pass through the membrane,but preferably prevents metal ions from passing. The purpose of themembrane is to keep the catholyte substantially free from the ions ofthe metal, which, if present, would be reduced at the cathode and willlead to its degradation. The membrane allows anions, such asmethanesulfonate, and sulfate to pass through the membrane, when currentis applied to the electrodes. In some implementations, water and acid(e.g., MSA) may also pass through the membrane, when current is applied.Examples of suitable anionic membranes include polymers functionalizedwith quaternary ammonium moieties, provided on a support structure. Oneexample of such polymeric functionalized anionic membrane is Fumasep®FAB-PK-130 PEEK (polyether ether ketone) reinforced anion exchangemembrane available from Fumatech of Bietigheim-Bissingen, Germany.

One embodiment of an electrolyte generating apparatus is illustrated byFIG. 2, which shows a cross-sectional schematic view of an apparatuswhere the anode-holding chamber 201 and a cathode-holding chamber 203are directly separated by an anion-permeable membrane 205. The low alphatin anode 207 resides in anolyte 209, which initially (before current isapplied to the electrodes) is composed of an aqueous solution of acid(e.g., methansulfonic acid and/or sulfuric acid), and, in someembodiments, may include Sn²⁺ ions in addition to the acid. As the anode207 is dissolved during the electrolyte generating process, theconcentration of Sn²⁺ ions in the anolyte is increased. Theconcentration of the tin ions is measured during the generation processby a densitometer 211, which is in communication with the controller213. Alternatively, the concentration of the tin ions is measured by acombination of a densitometer and a conductivity meter. The anolytechamber 201 has an inlet 215 for receiving an aqueous solution of acid(e.g., methanesulfonic acid or sulfuric acid) from the source of acid217, and deionized water from the source of deionized water 219. Inthose embodiments, where the anolyte initially contains a solution ofSn²⁺ ions, a pre-made, or commercially available solution containing tinsalt and, preferably, an acid is initially added through the inlet tothe anolyte chamber to bring the starting concentration of tin ions andacid to a desired range.

The anolyte chamber 201 further includes an outlet 221 for removinganolyte 209 to an electrolyte storage tank 223 (e.g., when theconcentration of tin ions reaches a target concentration), or to adrain. In some embodiments, there is also an anolyte recirculation loopassociated with the anolyte chamber. Portions of the anolyte can beremoved from the anolyte chamber through the outlet, and afterfiltration they can be returned to the anolyte chamber through theinlet.

The catholyte chamber 203 contains the catholyte 225 (typicallycontaining the same type of acid as the anolyte, but often at a higherconcentration) and a hydrogen generating cathode 227. In the depictedexample the catholyte chamber has an inlet 229 for receiving acid fromthe source of acid 217, and deionized water from the source of deionizedwater 219. In some embodiments the catholyte chamber further includes anoutlet, and an associated fluidic conduit that allows for removal ofportions of catholyte to a drain. The membrane 205 is permeable toanions but is substantially non-permeable to metal cations. Therefore,the concentration of tin ions in the catholyte is kept at a negligiblelevel. A power supply 231 is electrically connected with the anode 207and the cathode 227, and is configured to bias the cathode negativelyrelatively to the anode and to cause dissolution of the tin anode intothe anolyte. The controller 213 is in communication with theelectroplating apparatus and has program instructions for adjusting anyof the parameters of electrolyte generating process, such as removal ofelectrolyte from the anolyte chamber to the electrolyte storage tank,addition of acid and water selectively to anolyte and catholyte,duration of application of current by the power supply, the level ofcurrent that is being applied, etc.

The electrolyte generating apparatus shown in FIG. 2 can be improved inone or several aspects, according to several embodiments providedherein. The improvements may relate to management of tin iondistribution in the electrolyte, automation of reagent dosing andfeedback, removal of released hydrogen, and management of released heat.It is understood that not all of the improvements described withreference to FIGS. 3-5 need to be present in a single apparatus, as theapparatus may include any combination of features described herein.

It was observed that a single anion-permeable membrane between theanolyte chamber and the catholyte chamber may not be entirely sufficientfor blocking tin ions from migrating from anolyte to catholyte. Thepresence of tin ions in the catholyte is highly undesirable, as theytend to be reduced to tin metal at the cathode and, in large quantities,can make the cathode unusable. In order to address this problem, anapparatus configuration with one or more additional catholyte chambersin addition to the cathode-housing catholyte chamber is provided. Thus,such apparatus includes a first catholyte chamber configured to containa first catholyte and separated from the anolyte chamber by a firstanion-permeable membrane, and a second catholyte chamber configured tocontain the cathode and a second catholyte, wherein the second catholytechamber is separated from the first catholyte chamber by a secondanion-permeable membrane. Both anion-permeable membranes are configuredto impede migration of cations, such as tin ions, through the membrane,and, therefore, migration of tin ions to the cathode will besignificantly less pronounced than in a configuration with a singlemembrane. It is understood that the membrane separating the firstcatholyte chamber and the anolyte chamber may separate them directly orindirectly. When the separation is direct, the anolyte chamber isdirectly adjacent to the first catholyte chamber. When the separation isindirect, one or more additional catholyte chambers may be presentbetween the first catholyte chamber and the anolyte chamber.

In one embodiment the electrolyte generating apparatus is equipped witha catholyte-to-anolyte cascade where the apparatus includes a fluidicconduit that is configured for delivering catholyte from the firstcatholyte chamber to the anolyte chamber. The purpose of this conduit istwofold. First, it can be used to replenish the anolyte with acid (sincecatholyte is an acidic solution in an embodiment, where acidic tinelectrolyte is generated). It can be used instead of or in combinationwith the direct addition of acid to the anolyte from an external acidsource. Secondly, the first catholyte chamber can contain a small amountof tin ions that could have inadvertently migrated through the firstanion-permeable membrane. The removal of a portion of the firstcatholyte helps flush the tin ions from the first catholyte, therebyreducing the possibility of tin ion migration through the secondanion-permeable membrane to the cathode-housing second catholytechamber. This apparatus configuration is illustrated in FIG. 3A, whichshows a schematic cross sectional view of an electrolyte generator,having a catholyte-to-anolyte cascade and an anolyte cooling capability.

Referring to FIG. 3A, the apparatus includes a large anolyte chamber301, which houses the low alpha tin anode 303 and an anolyte. Theanolyte chamber can be divided into two sections: section 305 in theproximity of the anode reaction zone, and section 307, which isprimarily dedicated to cooling of the anolyte with a cooling structure309. While section 305 and section 307 are not separated by a membranein the depicted embodiment, the diffusion between these sections is notvery fast, and the apparatus includes a fluidic conduit 311 with anassociated pump (not shown), which is configured to deliver anolyte froman anolyte outlet 313 in section 305 to an anolyte chamber inlet 315 inthe cooling section 307. The transfer of anolyte within the anolytechamber from the proximity of the anode to the cooling section isperformed to facilitate heat exchange and cooling of the anolyte,(heated due to ohmic heat generated in the resistive electrolyte), andfurther to speed up mass transfer of anolyte in the anolyte chamber inorder to avoid fluctuations of tin ion concentration at differentportions of the anolyte chamber and to ensure accurate measurement oftin ion concentration. The anolyte outlet 313 is also connected with afluidic conduit to an electrolyte product storage tank 319, and theapparatus is configured to deliver the anolyte to the electrolyteproduct storage tank 319, when desired. For example, the apparatus maybe configured to deliver anolyte to the storage tank after concentrationof tin ions in the anolyte reaches a target concentration (for example,after a defined amount of charge has passed through the apparatus, andthe densitometer has confirmed that a target concentration range hasbeen reached).

The apparatus depicted in FIG. 3A has a removable cathode-housingassembly 321, which includes a first catholyte chamber 323, and a secondcatholyte chamber 325, where the second catholyte chamber 325 houses thecathode 327. The assembly 321 can be inserted into the anolyte chamberbetween section 305 and the cooling section 307, and can be releasablyattached to the anolyte chamber. The positioning of the cathode-housingassembly and the fact that it is removable offer a number of advantagesincluding compactness, design simplicity, and ergonomic access for bothanolyte and catholyte chamber maintenance. Furthermore, such designeliminates the need for a sealing between anolyte and catholytechambers.

The cathode-housing assembly is equipped with a first anion-permeablemembrane 329 that, in the depicted embodiment, directly separates theanolyte chamber and the first catholyte chamber. The membrane can bemounted onto a wall having one or more openings that are covered by themembrane after the membrane is mounted. The first catholyte chamber 323and the second catholyte chamber 325 are separated by a secondanion-permeable membrane 331, which may also be mounted onto a wall withopenings. The first catholyte chamber has an outlet 333, and a fluidicconduit 335, which is configured to deliver the catholyte from the firstcatholyte chamber 323 to the anolyte chamber through an anolyte chamberinlet 337. For example, the anolyte may be dosed with the firstcatholyte from the first catholyte chamber, if the concentration of acidin the anolyte becomes too low, because, in the depicted embodiment thefirst catholyte is more acidic than the anolyte, and can be used as thesource of acid. The anolyte may be also dosed with the first catholytefrom the first catholyte chamber when tin ions that inadvertentlymigrate from the anolyte through the first membrane need to be flushedfrom the first catholyte chamber. When the first catholyte istransferred from the first catholyte chamber to the anolyte chamber, thelevel of the first catholyte would drop and the first catholyte wouldneed to be replenished. In the depicted embodiment the first catholyteis replenished via a fluidic conduit 339, which connects the secondcatholyte chamber with the first catholyte chamber. In some embodiments,the fluidic conduit 339 is a hollow tube that is open from both ends,and which permits the second catholyte to automatically transfer to thefirst catholyte chamber, until the pressure in both chambers isequalized. In some embodiments the fluidic conduit 339 is a long andnarrow line, which impedes diffusion of the first catholyte into thesecond catholyte chamber, and thereby impedes inadvertent transfer oftin ions into the second catholyte chamber.

The second catholyte chamber has an inlet and a fluidic conduit 341coupled with this inlet, where the fluidic conduit is connected with asource of acid 343, and a source of water 345. Acid and water can beadded through the conduit 341 to the second catholyte in the secondcatholyte chamber, as desired. The source of water 345, in the depictedembodiment, is also fluidically connected via a conduit 347 to theanolyte chamber, and the apparatus allows for water dosing into theanolyte. The tin anode 303 and the cathode 327 are electricallyconnected to a power supply 349, which is configured to bias the anodepositively at a potential that is sufficient to cause dissolution of theanode.

The fluidic configuration shown in FIG. 3A is referred to as a cascadeconfiguration. In this configuration the second catholyte cascades fromthe second catholyte chamber through conduit to the first catholytechamber, and the first catholyte, in turn, cascades from the firstcatholyte chamber through conduit to the anolyte in the anolyte chamber.The second catholyte chamber is fed with acid and water through thesources of acid and water.

In one modification of the cascade configuration, the apparatus furthercomprises a fluidic conduit connecting the source of acid 343 with theanolyte chamber 301. Thus, in this configuration, the anolyte canreceive acidic solution both from the first catholyte chamber and fromthe source of acid. In some embodiments the source of acid is aremovable tote that is fluidically connected to the anolyte chamber anda second catholyte chamber through a buffer tank, that is configured toprovide an uninterrupted supply of acid.

In an alternative fluidic configuration, depicted in FIG. 3B, theapparatus comprises a fluidic conduit connecting the source of acid 343with the anolyte chamber 301, but does not have the conduit 335connecting the first catholyte chamber with the anolyte chamber. Insteadthe apparatus includes a fluidic conduit 336 connected with the firstcatholyte chamber at the outlet 333 and configured to deliver a portionor all of the first catholyte to drain, or for recycling it outside theelectrolyte generating apparatus. In this configuration, the anolyte isreplenished with acid only from the source of acid 343.

In the configurations shown in FIGS. 3A and 3B, the first catholytechamber 323 does not have a dedicated inlet for introduction of acidicsolution, and, instead, receives all necessary acid from the secondcatholyte chamber 325 through the conduit 339. In an alternative fluidicarrangement (which is applicable to both configurations shown in FIGS.3A and 3B), the conduit 339 is absent, and instead the first catholytechamber 323 contains an inlet in fluidic communication with an acidsource 343, and the apparatus is configured to dose the first catholytein chamber 323 with an acid from this source. Optionally, the source ofwater 345 may be also fluidically connected to the first catholytechamber inlet in this embodiment, and the apparatus may be configured todeliver water to the first catholyte chamber when needed.

It is noted that, in some embodiments, the same cascading principle thatis illustrated in FIG. 3A can be applied for modification of anapparatus having a single catholyte chamber shown in FIG. 2. In someembodiments, this apparatus is equipped with a fluidic conduit (otherthan a membrane) that is configured to deliver catholyte to anolyte.This fluidic conduit may be used instead of the acid source—to—anolytedelivery line or in addition to this delivery line. In an alternativeembodiment the apparatus shown in FIG. 2 includes a fluidic lineconfigured to deliver portions of catholyte to waste or for recyclingoutside of the apparatus.

In addition to the fluidic lines shown in FIGS. 3A and 3B, the apparatusmay include an anolyte recirculation and filtration system that isconfigured to remove portions of anolyte from the anolyte chamber, andreintroduce the anolyte into the anolyte chamber after filtration.Further the apparatus may include fluidic lines configured for removingportions of electrolyte (e.g., anolyte, first catholyte, secondcatholyte and combinations thereof) to a drain if needed.

The fluidic lines described with reference to FIGS. 3A and 3B arecoupled to a pump or pumps and can be used in conjunction with valves orvalve manifolds that allow for controlled selective introduction offluids to different destinations. These pumps, valves and associatedflow meters are not shown to preserve clarity. In some embodiments, theapparatus is configured to separately control each of the fluidicstreams. For example, the timing of dosing of fluids, and the amount ofdosed fluids can be separately controlled with a combination of flowmeters and valves, connected with a system controller. In someembodiments, all of the fluidic conduits shown in FIG. 3A and FIG. 3Bwith the exception of conduit 339 that connects the first and secondcatholyte chambers, are coupled with pumps and are equipped with valvesthat are configured to keep the conduits open and closed. The conduit339, in some embodiments, functions without a pump or a valve, and themovement of the second catholyte to the first catholyte chamber isachieved solely due to the pressure differential between the first andsecond catholyte chambers. In some embodiments, one or more fluidicconduits of the apparatus are connected with filters, and allow forfiltration of various fluidic streams in the system. For example, theanolyte directed from the anolyte chamber to the electrolyte storagetank, in some embodiments, is passed through a filter before it entersthe electrolyte storage tank to remove any insoluble impurities.

In some embodiments the apparatus presented herein, is furtherconfigured to deoxygenate the electrolyte. Deoxygenation is preferablyperformed in the anolyte chamber, and is primarily used to preventoxidation of Sn²⁺ ions to Sn⁴⁺ ions. Formation of Sn⁴⁺ ions is highlyundesirable, because it can lead to precipitation in the electrolyte andgenerally to deterioration of quality of the formed electrolyte. In someembodiments deoxygenation is performed by bubbling an inert gas (e.g.,nitrogen or argon) through the anolyte, e.g., in the anolyte chamber.Thus, in some embodiments, the apparatus includes a conduit connected toa source of an inert gas that is configured to bubble the inert gasthrough the anolyte in the anolyte chamber. Further, in someembodiments, similar deoxygenation is also performed in the electrolytestorage tank, and, in some cases, in the catholyte chamber (e.g., firstand/or second catholyte chamber).

The fluidic features of the electrolyte generating apparatus, in someembodiments, communicate with a system controller, where the controlleris also configured to communicate with one or more sensors of theelectrolyte-generating apparatus. The sensors provide feedback to thecontroller, which is programmed with the instructions to adjust one ormore process parameters in response to the data provided by the sensors.FIG. 4 provides a cross-sectional schematic view of anelectrolyte-generating apparatus, illustrating different types ofsensors that can be used to provide data to the controller foraccomplishing fully or partially automated generation of theelectrolyte. The apparatus shown in FIG. 4 is similar to the apparatusof FIG. 3A, and it is understood that the fluidic features shown in FIG.3A and FIG. 3B are to be used with one or more sensors shown in FIG. 4.The apparatus shown in FIG. 4 differs from the apparatus shown in FIG.3A, in that the low alpha tin anode in FIG. 3A is a single piece of lowalpha tin metal (available from Mitsubishi Materials Corporation ofTokyo, Japan or Honeywell International, Inc. of Morristown, N.J.),whereas the apparatus shown in FIG. 4 employs a plurality of low alphatin pellets placed in an ion-permeable container, where the pelletsserve as an anode. Typically the pellets are smaller than 6 mm(referring to the largest dimension), for example, smaller than 3 mm.The pellets can be cylinders, spheres or particles of any other shape,including mixtures of randomly shaped pellets. One specific example ofsuitable pellets are cylindrical pellets, where each pellet is about 2.5mm in diameter and is about 2.5 mm long. Alternatively, round pellets ofnominally the same dimension are used. Both types of the anode can beused in apparatuses having fluidic features shown in FIG. 3A and FIG. 3Band with sensors shown in FIG. 4 (with the exception of pellet levelsensor, which is used only for pellet-based anode).

Referring to FIG. 4, the apparatus includes an anolyte chamber 301 and agravity fed hopper 401 that provides low alpha tin pellets into theanode container 403. A charge plate in electrical communication with thepower supply 349 is integrated with the anode container 403, and servesto electrically bias the low alpha tin pellets covered with the anolyte.The pellets wetted with the anolyte and biased by the charge platecollectively serve as an anode 303, and are dissolved to form tin ionswhich are released into the anolyte during the electrolyte-generatingprocess. Therefore, in order to release tin ions into the anolyte theanode container 403 is permeable to ions. In some embodiments the chargeplate serves as the anode container. In other embodiments, the containeris an ion-permeable membrane (e.g., made of a polysulphone material)that does not serve as a charge plate, while the anode is biased using aconducting rod that contacts the pellets and that is connected to thepower supply.

Tin pellets are loaded into the gravity hopper 401, and the level of tinpellets gradually moves down, as the anolyte-covered pellets aredissolved during electrolyte generation, and the dry pellets from thehopper settle down under the force of gravity, become covered with theanolyte and start functioning as the anode. The apparatus shown in FIG.4 includes a sensor 405 configured to determine if the pellets havesettled below a critical level, and to signal that replenishment of thepellets is needed if they did. The sensor 405 may be an optical sensoror a capacitive sensor, such as an optical through-beam sensor or acapacitive sensor available from Balluff Inc. of Florence, KY. Thereplenishment of the hopper with tin pellets can be carried outautomatically or manually. For example, after the level of pellets isdetermined by the sensor to be critical, the hopper may be manually orautomatically reloaded with between about 5-30 kg of tin pellets.

The anolyte chamber 301, in the depicted embodiment further includes asensor (one or more sensors) for determining the concentration of tinions 407, a sensor (one or more sensors) for determining theconcentration of acid 409, and an anolyte level sensor 411. In one ofthe preferred embodiments, a densitometer is the sensor primarily usedto determine concentration of tin ions, and a conductivity meter is thesensor primarily used to determine the concentration of the acid in theanolyte. It was observed that the density of the anolyte depends to agreater degree on the concentration of the tin ions than on theconcentration of the acid, and that concurrent measurement of anolytedensity and anolyte conductivity can be used to accurately determineconcentrations of both tin ions and acid in the anolyte. The densitiesand conductivities of electrolytes at different tin ion concentrationsand acid concentrations can be pre-tabulated for different types of acidand can be used by the controller to determine the actual concentrationsof tin ions and acid from the data provided by the conductivity sensorand the densitometer. Alternatively, the controller can be programmedwith density and conductivity values that correspond to targetconcentration ranges, and actual calculation of the concentration may beunnecessary. An example of a suitable densitometer is a Micro-LDSdensitometer available from Integrated Sensing Systems of Ann Arbor,Mich., or a similarly capable device available from Anton-Paar ofAshland, Va. It was discovered that in highly conductive electrolytesolutions, such as in acidic electrolyte solutions, it is preferable touse inductive conductivity meters, such as a toroidal conductivitysensor (e.g., model 228, available from Rosemount Analytical (EmersonProcess Management) of Irvine, Calif.). While in some embodiments, moreconventional conductivity meters that rely on measuring conductivitybetween two electrodes can be used, the inductive conductivity metershave the advantage of being more compact since in highly conductivesolutions the distance between electrodes should be quite large in orderto obtain an accurate measurement. It is understood that alternativemeasuring sensors or system can be used to measure intrinsic propertiesof the anolyte (spectrophotometers, refractive index sensors, IR orRaman spectroscopy equipment), or a combination of sensors (for example,balance/weight sensors in combination with a fluid volume sensor) canalso be used. The anolyte level sensor 411 is configured to determine ifthe level of anolyte drops below a critical level. The anolyte levelsensor 411, in some embodiments, is an optical sensor.

The second catholyte chamber 325 includes a sensor 413 configured tomeasure acid concentration (e.g., an inductive conductivity sensor) anda catholyte level sensor 415 (e.g., an optical sensor) configured todetermine when the level of catholyte in the catholyte chamber fallsbelow a critical level. The sensors 405, 407, 409, 411, 413 and 415 arein communication with the controller 417, which receives and processesdata from the sensors.

In some embodiments, the electrolyte generating apparatus providedherein is equipped with a hydrogen management system. Because the inertcathode in the catholyte chamber generates hydrogen gas, which can formexplosive mixtures with air, it is advantageous to provide a hydrogenmanagement system that is configured for diluting hydrogen to a safeconcentration (well below lower explosion limit or LEL), and forremoving diluted hydrogen out of the apparatus. The hydrogen managementsystem can be integrated with an apparatus having a single catholytechamber (such as with an apparatus shown in FIG. 2), or with anapparatus having multiple catholyte chambers (such as with an apparatusshown in FIG. 3A and FIG. 3B).

In one implementation the hydrogen management system includes a diluentgas conduit configured to deliver a diluent gas to a space above acatholyte, and to dilute hydrogen gas accumulating in that space,wherein the space above the catholyte is covered with a first lid havingone or more openings that allow for transfer of diluted hydrogen into aspace above the first lid. For example, in the apparatus shown in FIG.3A and FIG. 3B, such lid can cover the second catholyte chamber thathouses the cathode generating hydrogen gas. In some embodiments, thehydrogen management system further includes a second lid over the firstlid and spaced apart from the first lid such that there is a spacebetween the first and second lids; and a second diluent gas conduitconfigured to deliver a diluent gas to a space between the first andsecond lid and to move the diluted hydrogen gas from the space betweenthe first and second lids towards an exhaust. The diluent gases providedthrough the first and second conduits may be the same or different. Adiluent gas may be a mixture of gases or a single gas. Examples ofdiluent gases include air and inert gases, such as nitrogen and argon.In one of the preferred embodiments, an inert gas, such as nitrogen orargon is used as first diluent gas to ensure safe first dilution ofhydrogen below the LEL. After the hydrogen has first been diluted withan inert gas, air can be safely used as the second dilution gas. Inanother embodiment, inert gases are used both as the first and seconddilution gases.

FIG. 5 provides a schematic cross-sectional view of an example of acatholyte chamber equipped with a hydrogen management system. Thecatholyte chamber 501 houses an inert hydrogen generating cathode 503immersed into a catholyte (shown at a fluid level 505). The catholytechamber has an inlet 507 connected with a diluent gas conduit 509, andis configured to admit the diluent gas provided from the source of thediluent gas 511 through this inlet into the space above the catholyte. Afirst lid 513 is disposed above the catholyte and has one or moreopenings 515 through which the diluted hydrogen gas is transferredupward. A second lid 517 is disposed above the first lid 513, and thespace between the first and second lids is equipped with an inlet 519,coupled with a diluent gas conduit 521 configured to deliver a diluentgas from the source of diluent gas 511 into this space and to move thediluted hydrogen gas through this space in a horizontal directiontowards the exhaust 523, which removes the diluted hydrogen gas from theapparatus.

A specific example of an electrolyte-generating apparatus is illustratedby FIGS. 6A-6I, and FIGS. 7A-7C. FIGS. 6A and 6B provide side views ofthe apparatus (from two opposite sides), FIG. 6C provides across-sectional view of the apparatus, and FIG. 6D provides anothercross-sectional view. FIG. 6E provides a perspective view of theapparatus.

The illustrated apparatus includes a removable cathode-housing assembly,where the assembly has a first catholyte chamber and a second,cathode-housing catholyte chamber, wherein the two chambers areseparated by an anion permeable membrane. The apparatus is equipped witha catholyte-to-anolyte fluidic cascade, a two-lid hydrogen managementsystem, and a cooling system. FIGS. 6F-6I show different views of thecathode-housing assembly, where FIG. 6F shows an isometric view of thecathode-housing assembly, while FIGS. 6G-6I show differentcross-sectional views of the same assembly illustrating differentaspects of the hydrogen management system. FIGS. 7A-7B provide views ofthe interface between the anolyte chamber and the first catholytechamber. FIG. 7C illustrates a part of the apparatus showing anembodiment with a gutter for removing overflow anolyte to a filtrationassembly.

The apparatus shown in FIGS. 6A-6E combines a number of advantageousfeatures. The apparatus includes two anion-permeable membranesseparating the anode and the cathode (as previously illustrated bymembranes 329 and 331 in FIG. 3A and FIG. 3B). When a single separatoris used as shown in the embodiment illustrated in FIG. 2 (assuming theseparator is an anion-permeable membrane), the separator is often notcompletely impermeable to tin ions. Therefore, tin ions can migrate fromthe anolyte to catholyte and poison the cathode. The embodimentsillustrated by FIG. 3, and FIGS. 6A-E provide an additional, middlecatholyte chamber that can be flushed with acidic solution to remove anytin ions that inadvertently migrated into the middle catholyte chamber.In the depicted embodiment the catholyte from the first catholytechamber (middle chamber) is transferred to the anolyte chamber, whilethe middle chamber is replenished with the catholyte derived from thesecond catholyte chamber. In such reverse double membrane cascading, twoanionic membranes that inhibit the migration of metal cations (and to alesser extent protons from the acid) are employed as a preferredseparator.

While in some embodiments provided herein, the apparatus includes asolid single-piece anode (as illustrated in FIG. 2 and FIGS. 3A and 3B),the use of solid metal anode does not allow for efficient automaticreplenishment of anode material. In some embodiments provided herein(illustrated in FIG. 4, and in FIGS. 6A-6E) this problem is addressed byproviding a gravity hopper containing metal pellets. The hopper feedsthe pellets into the anode active zone as the anode material is beingdissolved. That is, there are dry metal pellets on the top of the hopperwhich feeds directly into the anode active zone where the pellets arewetted by the electrolyte. As the wet anode pellets are dissolved in thereaction, the dry pellets shift under gravity into the anode activezone, are wetted and are dissolved during the reaction.

Further, as it was previously noted, the generation of hydrogen gas atthe cathode can be hazardous because the mixture of hydrogen with aircan be explosive. In some embodiments (illustrated in FIGS. 6A-6F) theapparatus includes a double lid design that is configured to keep thecomposition of hydrogen-containing gas at a safe specification. Forexample a conduit for delivering an inert gas (e.g., N₂) into theapparatus may be used.

Finally, in the apparatus illustrated by FIGS. 6A-6F, a number offeatures that are configured for providing automated electrolytegeneration, storage, and delivery, are provided.

Referring to FIGS. 6A-6F, the automated electrolyte distribution andgenerator equipment is provided. The equipment includes an electrolytegenerator 600, in fluidic communication with an electrolyte storage tote601 configured to accept the generated electrolyte from the generatorand to store the generated electrolyte. The generator is also in fluidiccommunication with a concentrated acid tote 603 that is configured todeliver the concentrated acid via line 604 to the electrolyte generator600. In other embodiments, the generator is in communication with theconcentrated acid tote through an acid buffer container, which allowsfor the tote to be replaced or replenished without stopping theelectrolyte generation process. In some embodiments the concentratedacid tote or a buffer container contains an aqueous solution of MSA,sulfuric acid, sulfamic acid or any combinations of these acids. In onespecific embodiment the concentrated acid solution consists essentiallyof MSA solution having a concentration of between about 900-1000 g/L. Inthe depicted embodiment, the electrolyte generator 600 includes aself-regulating gravity-feeding hopper 605 that meters the flow of metal(e.g. low alpha tin) pellets into a vertical porous bed of metal anodereactant, forming an anode reactant column 606. In other embodiments anauger-regulated hopper may be used. As the pellets are consumed duringthe electrochemical dissolution of pellet-based anode, they are replacedby fresh pellets from above. The apparatus further includes a pelletrestraining and/or retaining charge plate 607 electrically connectedwith an anode power buss that is electrically connected to a powersupply that positively polarizes the anode pellet bed. In the depictedembodiment, the charge plate serves to both physically contain thepellets of the anode in place and to conduct charge from the power bussto the pellets and to provide ionic communication between the pelletsand the anolyte, such that the generated metal ions could be releasedinto the anolyte. Accordingly, in the depicted embodiment, the chargeplate is a porous, ionically permeable, electrically conductive elementthat is insoluble under electrolyte generation conditions (also referredto as inert). In other embodiments, the pellets are contained with anion-permeable membrane (e.g., made of a polyethersulphone material),which can be reinforced with a support structure, but does notnecessarily need to be connected to a power buss and serve as a chargeplate. In this embodiment charge is delivered by the electricallyconductive buss bars contacting the pellets and connected to the powersupply. In some embodiments the apparatus includes inert currentcollector buss bars and a fine anode membrane (e.g. a porouspolyethersulphone (PES) membrane) with a support frame configured tocontain the anode pellets, and may optionally include a conductiveporous current collector mesh screen (charge plate) electricallyconnected to the buss bars.

The apparatus further includes an anode bed recirculating flow feedinginjection manifold 609, which is configured in the illustratedembodiment to force a portion or all of the recirculating anolyte flowto move from the bottom of the anode upwards. This anolyte then exitsthe anolyte chamber through a porous weir and a gutter at the top of theelectrolyte generator, is filtered, and is then returned to the anolytechamber at the bottom portion of the anode bed with the manifold 609.

The gravity hopper, in some embodiments further includes a sensor orsensors (e.g., capacitive or optical sensors) to indicate to systemcontroller and/or apparatus operator when the hopper metal pellet supplyis low and needs replenishment.

In the depicted embodiment, the anode bed is a fixed packed bed, wherethe metal granules are packed by gravity and are wetted by the anolytesolution injected from the bottom portion of the bed. In the depictedembodiment the granules are not substantially moved by the flow of theanolyte. In alternative embodiments, a fluidized bed of metal particlescan be used. In the fluidized bed, the metal particles are not packedbut are continuously moving as they are impacted by the flow of theanolyte. The use of a packed fixed bed offers several advantages overthe use of a fluidized bed. First, it is easier to ensure electricalcontact of the particles in a packed bed than in a fluidized bed.Secondly, the use of fluidized bed requires a metering device foraddition of particles. In the absence of such metering device, additionof too many metal particles will result in the loss of particle mobilityleading to transformation of the bed to a non-fluidized packed form. Iftoo few particles are added, the particles in the fluidized bed wouldnot be able to make sufficient electrical contact with the charge plateand with each other. Therefore, in a fluidized bed, instead of aself-regulating gravity hopper, a hopper with a metering device, such asan auger hopper or a metering gate/valve, should be used, in order toprovide a required amount of particles into the bed to accuratelycompensate for the calculated amount of consumed metal. In contrast,when a fixed, packed bed is employed, the metal particles can be fedthrough the gravity hopper, which automatically replenishes consumedparticles. The additional particles can be added to the gravity hopperwhen the hopper sensor indicates that the level of the particles in thehopper is too low, but the amount of added particles need not exactlymatch the amount of consumed particles in the packed bed embodiment. Thefluidized bed further can give rise to problems related with differentsizes of the particles. As the particles are consumed, smaller particleswill tend to rise and new added particles will tend to drop to thebottom in the fluidized bed, which can lead to destabilization of thebed. Further, particles of different sizes will be fluidized differentlyby the stream of anolyte in a fluidized bed, and velocities of suchdifferent particles may be difficult to control.

The depicted apparatus further includes a removable cathode-housingassembly 611, which is inserted into the anolyte chamber 613. Thecathode-housing assembly 611 has two chambers, separated from each otherby an anion-permeable membrane. The first catholyte chamber 615 (alsoreferred to as middle chamber) is separated from the anolyte chamber 613by a first anion-permeable membrane 617. The second catholyte chamber619 is separated from the first catholyte chamber 615 by a secondanion-permeable membrane 621, and is configured to house an inerthydrogen generating cathode 623. The separation does not need to becomplete (prevent all fluid motion under pressure gradients), and insome embodiments, there is a long and narrow channel (641) that allowsfor fluidic communication and pressure equalization between the firstand second catholyte chambers while simultaneously presenting a longdiffusion path for transport of compounds located in the middle chamber(e.g. Sn⁴⁺ byproduct and Sn²⁺ metal that leaks to the mid chamber) fromreaching the second cathode chamber. The cathode-housing assembly 611(including the first catholyte chamber 615 and the second catholytechamber 619) is removable as a complete sub-assembly from theelectrolyte generator 600 and anolyte chamber 613. The cathode-housingassembly 611 is designed to be installed in an opening from above andinto the anolyte chamber 613, fitting within the contained volume of theanolyte chamber. The anolyte chamber 613 contains sufficient volume andnecessary hardware to allow the insertion, mounting, and removal of thecatholyte chamber. The anolyte chamber 613 includes various processmonitoring sensors, deoxygenating features and features for maintain lowoxygen concentration in the anolyte. For example, an inert gas bubbler624, connected with a source of an inert gas, such as argon or nitrogen,may be placed in the anolyte chamber, and may be configured to bubbleinert gas through the anolyte for anolyte deoxygenation purposes. Theanolyte chamber 613 may be configured for removal of process heat andmay include a heat exchanger 625. In the illustrated embodiment theapparatus is also configured for measuring concentrations of anolytecomponents during electrolyte generation. The concentrations aremeasured by measuring the density of the anolyte with a densitometer andalso measuring the conductivity of the anolyte with a conductivitymeter, such as the anolyte conductivity meter 626. These two parameters(density and conductivity) can be combined and the concentration ofmetal ions and the concentration of acid in the anolyte can becalculated based on these parameters. The calculated concentrations fromthese two parameters (or the parameters themselves) are used to monitorand run the electrolyte generation process so that the product(electrolyte) is manufactured with concentrations of components fallinginto target ranges. The calculation and/or determination of whether themeasured parameters are within the target ranges can be performedautomatically by the controller. The anolyte chamber 613 contains avolume sufficient to accept the anode and associated hopper, theremoveable cathode-housing assembly, and also has a volume for storingthe generated anolyte (where cooling of the anolyte, deoxygentaion ofanolyte, and measurement of anolyte parameters, such as density,conductivity, pH, and optical absorbance takes place). In the depictedembodiment the anolyte chamber 613 can be viewed as having a portion 627proximate the anode and a cooling portion 629, arranged such that thecathode-housing assembly 611 resides between these two portions.

In the depicted embodiment the apparatus is further equipped with amechanism and fluidic features to enable cascade of catholyte (whichconsists essentially of acid with no more than a trace amount of tinions) from the first catholyte chamber (middle chamber) to the anolytechamber. This cascade is advantageous for impeding transport of tin ionstowards the cathode, as it can prevent the tin ions from reaching thehydrogen generating cathode. Thereby tin plating on the cathode and lossof cathode efficiency can be avoided. Further, this cascade preventsparticle generation in the second cathode-housing chamber, since tinparticles could form if tin ions are reduced in the cathode-housingchamber. Therefore, such cascade increases the life of the electrolytegenerator between operator interventions and maintenance. In analternative embodiment, portions of catholyte from the first catholytechamber are removed from the mid chamber and transferred to waste (to adrain), and the first catholyte chamber is charged with fresh acid,thereby resulting in a decrease of residual tin ion concentration in thefirst catholyte.

Referring to side views of the generator (FIGS. 6A and 6B), theelectrolyte generator 600 is shown in a simple generator containmentvessel, 630, which is optional. More typically, the containment is partof the overall tool and system enclosure that also houses electronics,programmable logic controllers (PLC's) and computers, chemical feedaccess points, and general facilitation, where general facilitationincludes sources of deionized water, supply of cooling water, sources ofcompressed dry air, sources of nitrogen, sources of electrical power,and exhaust.

A dosing and fluid transfer pump 631, shown in FIG. 6A as attached tothe wall of the generator, is connected to a number of pump-source andpump-destination control valves (e.g. 633 and 635), so that this singlepump can serve multiple generator-relevant fluid transferringoperational tasks at different times in the generation process. Thedosing and fluid transfer pump 631 is connected to a source ofconcentrated liquid acid feed stock 603. In some embodiments the sourceof acid 603 contains a concentrated acid (e.g. 98% sulfuric acid) or anaqueous acid solution (e.g., 70% methanesulphonic acid or 30% sulfamicacid solution). In alternative embodiments, depending on the type of theelectrolyte produced, a different type of feedstock solution may beloaded into the tote 603. For example, in some embodiments, when anon-acidic electrolyte is generated, a neutral salt solution, analkaline solution or a solution containing a metal chelator can beloaded into the feedstock tote. By setting the positions of thepneumatic valves to an appropriate combination of states, theconcentrated acid solution can be transferred from the acid tote 603 tothe cathode-housing assembly chamber 611, or to the anolyte chamber 613.The part of the total anolyte recirculation flow that returns to theanolyte chamber 613 without passing through the anode reaction zone 606is monitored by a flow meter 637 before or after being filtered byfilter.

The same dosing and transfer pump 631 is configured to draw a knownamount of fluid out of the cathode-housing assembly 611 and to move itto either a waste drain, or to the anolyte chamber 613. In an embodimentpreviously illustrated with reference to FIG. 3A, pump 631 drawscatholyte from the first catholyte chamber (mid chamber) of thecathode-housing assembly, and transfers the acidic catholyte to acidifythe anolyte product in the anolyte chamber 613.

This process serves three primary functions. First, because theanion-permeable membranes 617 and 621 are not always completelyeffective in inhibiting positive ions (metal and hydrogen ions) frommigrating across the membranes under the influence of the electric fieldapplied to the electrolytic cell, a small amount of migrated metal ionsand protons can transfer through the first anion-permeable membrane 617(closest to the anode) and can start to accumulate in the firstcatholyte chamber (middle chamber) 615. In order to avoid theaccumulation of metal ions in the first catholyte chamber 615 to a highenough concentration that would eventually allow them to move across thesecond membrane 621 to the second catholyte chamber 619 and be reducedto metal at the cathode in the second catholyte chamber 619, thecatholyte is periodically drawn from the first catholyte chamber 615 andis either sent to waste, or, in some embodiments, is transferred to theanolyte chamber 613. The first catholyte chamber 615 preferably containsa relatively small volume of catholyte relative to that in thecathode-housing chamber. In some embodiments the total volume ofcatholyte (including catholyte in the first and second chambers) isabout 30 L, of which the volume of the catholyte in the first chamber isonly 1.5 L. In some embodiments the volume of catholyte in the firstcatholyte chamber is less than about 20%, such as less than about 10% ofthe total volume of catholyte (catholyte in first and second chamberscombined). In some embodiments the volume of the first catholyte chamberin the apparatus is less than about 20%, such as less than about 10% ofthe total volume of the catholyte chambers. The small volume of thefirst catholyte chamber is advantageous because it allows for facileflushing of this chamber to remove tin ions, without having to transferlarge amounts of liquid. The existence of the first catholyte (middle)chamber 615 allows for the transfer of ionically or mechanically leakedmetal ions from catholyte back to the anolyte in such fashion that theleaked metal ions do not substantially come into contact with thecathode 623. This configuration greatly improves the robustness of theelectrolyte-generation process, reducing the maintenance labor andincreasing the long term reliability of the electrolyte generator.

The second advantage of the catholyte-to-anolyte cascade relates to acidmanagement. When the acidic catholyte is transferred from the firstcatholyte chamber 615 to the anolyte chamber 613, it functions toreplace the protons that are drawn out of the anolyte chamber into thefirst catholyte chamber during the electrolytic process. The physicaltransfer of acidic catholyte from the first catholyte chamber back tothe anolyte chamber is a cost effective way of reversing the effect ofthis anionic membrane proton “leakage”.

The third advantage of the catholyte-to-anolyte cascade also relates toreplenishment of anolyte with acid. When small batches of generatedelectrolyte are removed from the anolyte chamber to the storage tank,the lost volume needs to be replenished before the next batch ofelectrolyte is generated. If that anolyte volume decrease werecompensated for by solely adding water, the acidity of the anolyte willdrop. This drop in acidity can become significant and problematic afterseveral batches of electrolyte are generated and removed to the storagefrom the anolyte. If the acidity continues to fall, the solubility ofthe metal ions generated by the anode dissolution will tend to decrease.Therefore, transferring acidic catholyte from the first catholytechamber to the anolyte chamber serves the purpose of replenishing acidin the anode chamber and for maintaining the acid balance and processstability. Preferably, the acid balance in the anolyte is maintainedsuch that the acid content in the anolyte does not fluctuate by morethan 50% of a target level. For example, when MSA or sulfuric acid isused, preferably acid content should not fluctuate by more than 15 g/Lfrom a target concentration of 45 g/L during the electrolyte generationprocess (including during generation of individual batches and betweengeneration of the batches). Preferably, when tin electrolyte isgenerated, the acid content of the anolyte is not allowed to drop below15 g/L (referring to MSA or sulfuric acid content).

When the catholyte is drawn out of the first catholyte chamber, thelevel of catholyte in this chamber would decrease over time and thefirst catholyte chamber will eventually run completely dry. Therefore,the apparatus is equipped with fluidic features for replenishing thefirst catholyte chamber with acid and water. In one of the preferredembodiments, the first catholyte chamber is replenished via a fluidicconduit (other than a membrane) that fluidically connects the secondcatholyte chamber with the first catholyte chamber. In the illustratedembodiment the base of the cathode-housing assembly 611 contains a longand narrow conduit or channel 641 that fluidically connects the firstcatholyte chamber 615 with the second catholyte chamber 619. Forexample, the channel may be about 30.5 cm long having a cross sectionalflow area of less than 2 cm². This channel serves as a flow ballastconnection between the first catholyte chamber 615 and thecathode-housing second catholyte chamber 619, effectively working tokeep the levels of catholyte in the two chambers equal. In one of thepreferred embodiments, as catholyte is drawn out of the first catholytechamber 615 and is transferred to the anolyte chamber 613, the catholytein the cathode-housing assembly will spontaneously flow from the secondcatholyte chamber 619 (having a slightly higher level after thecatholyte is drawn from the first catholyte chamber) through theconnection conduit 641 and into the first catholyte chamber 615. In oneembodiment, the conduit inlet 643 is located at the base of thecathode-housing assembly and at the distal end relative to the firstcatholyte chamber, thereby maximizing the distance and diffusionresistance for any metal ions that could possibly move by diffusion downthe conduit 641, from the first catholyte chamber 615 into the secondcatholyte chamber 619 and reach the cathode 623. The volume and mass ofthe materials (e.g., water and acid) removed from the first catholytechamber are replaced by adding an equal volume and mass of materialsinto the second catholyte chamber, measured, for example, using thedosing and transfer pump 631. This can be accomplished by using anappropriate configuration of valves 633 and 635 configured to draw acidfrom the acid tote 603 and to transfer this acid to the second catholytechamber 619. In an alternative embodiment, the conduit 641 is absent,and fresh acidic solution and deionized (DI) water is added directly tothe first catholyte chamber from an acid supply and DI water supply.

The apparatus depicted in FIGS. 6A-6E is further configured forsupplying deionized water to both the anolyte chamber 613 and the secondcatholyte chamber 619. An anti-diffusion valve 645 is used incombination with other valves to direct DI water to catholyte or anolytechambers. The anti-diffusion valve 645 is designed to prevent waterstagnation and back-contamination of the DI water feed source. Theanolyte chamber 613 has a drain 647 at its base through which theanolyte is drawn out by the main circulation pump 649. The drawn anolytecan be directed via line 651 to any of a number of destinations. Whenthe anolyte reaches the required concentrations specified for generatedelectrolyte, the anolyte product from the anolyte chamber outlet can betransferred to the electrolyte storage container tote 601. If therequired concentration of metal ions in the anolyte is not reached, orif transfer of product is not desired for any reason, the anolyte fromthe outlet can be transferred to the cooling portion of anolyte chamber629, where the heat exchanger is located, or it can be injected backinto the anode porous bed region 606 of the anolyte. The direction ofthe anolyte flow from the outlet can be controlled by periodicallyadjusting the settings of the valves. For example, periodically therecirculating anolyte is directed to the electrolyte storage tote, ifthe anolyte has target concentrations of components.

A flow meter 653 measures the fraction of the total flow of the anolytethat is used for recirculation. That flow starts from the outlet 647 andpasses through the pump 649. The amount and/or fraction of flow going toeither the anode reaction zone 606 via a manifold at the bottom of thereaction zone, or to the cooling portion 629 of the anolyte chamber isregulated by a control valve 657. In the illustrated example thisregulation is accomplished by opening of a needle valve knob 659 of theanode reaction flow branch.

A diaphragm pump 661 is used for removing materials from the electrolytegenerator for maintenance and cleaning. Depending on the state of twoway valve 663, the pump 661 can remove catholyte via line 665 from thesecond catholyte chamber, or it can remove anolyte from the anolyteoutlet line before that line reaches the main circulation pump 649.

As it was previously mentioned, the metal pellets are supplied to theanode reaction zone 606 via a metal pellet hopper 605. The hopper has alid 667, and one or more surfaces slanted from top to bottom, such thatthe pellets supplied from the top opening are contained and the flow ofpellets is directed through the reaction chamber pellet entrance (orthroat) and into the anode reaction zone 606. When the electrolytegenerator is “on” and an anodic current and potential is applied to theanode buss 671, current passes onto the anode charge plate 607 and tothe pellets. Two anode busses 671 run along the periphery of the anodereaction zone 606 and pass through the plastic wall of the anode hopper605 using a connection bolt.

The apparatus illustrated in FIGS. 6A-6F is configured for maintainingthe level of hydrogen below the lower explosion limit (LEL). Theapparatus includes a main access lid 673 which covers the top of theelectrolyte generation reactor and is functional in controlling the flowof air, such that the hydrogen gas level in the chamber below the lidremains lower than the LEL for hydrogen in air. Dilution air (which actsas a diluent gas in this case) enters the chamber between the top lid673 and an inner lid 675 covering the cathode-containing assembly 611through a set of inlet openings 677, which are visible in the view ofthe apparatus shown in FIG. 6E The diluent gas moves substantiallyparallel to the horizontal plane in the space between the lids 673 and675, mixing with hydrogen-containing gas that exits the cathode-housingassembly 611 through openings 678 in the inner lid 675. The mixed gasthen reaches the exhaust manifold distribution plate 679, enters theexhaust manifold 681 and exits through the exhaust 683.

In the depicted embodiment, an additional flow of a diluent gas isdirected into the space above the catholyte above the cathode 623 andbelow the inner lid 675. The structure of the inner lid and of thecathode-housing assembly is visible in FIGS. 6F-6I. The second catholytechamber 619 contains a hydrogen-generating cathode 623 which is alsoreferred to as a dimensionally stable cathode (DSC), which generateshydrogen gas during electrolyte generation. The cathode has externalconnection buss points 685, which are connected to a power supply thatnegatively biases the cathode during electrolyte generation. Inert DSCcathodes are commonly used as a hydrogen generating electrodes inelectro-synthesis and fuel cell applications as a well as cathodes forthe chloro-alkali industry. These cathodes are distinct fromdimensionally stable anodes (DSA) that are commonly used inelectrowinning and chlorine production in the chloro-alkali industry.The DSC is commonly made of an underlying titanium or similarelectrochemically inert substrate or a plate that is coated with arelatively thin film (e.g., less than 100 microns thick, such as 10-90microns thick) of a material having catalytic properties for thereaction of water and acid electrolysis and more generally for hydrogenformation. Common coating materials include platinum, niobium,ruthenium, iridium dioxide, and mixtures thereof. During operation ofthe electrolyte generator, hydrogen bubbles are formed at the cathode623 in the gap 687 between the anode-facing surface of the cathode andthe second anion-permeable membrane 621. The atmosphere in thecathode-housing assembly 611 below the inner lid 675 is composed of amixture of hydrogen generated at the inert cathode 623 and a diluent gas(e.g., diluent air) that is introduced into the cathode-housing assemblyvia line 689, through fitting 691 and through catholyte chamber manifold693. The diluent gas is introduced uniformly just above the location ofthe emerging hydrogen bubbles through a set of manifold hole 695. Theflow rate of the diluent gas is configured such that it will result in ahydrogen concentration in the chamber below the inner lid (assumingcomplete and uniform mixing) well below the lower explosion limit ofhydrogen. In some embodiments the concentration of hydrogen under theinner lid is 4 times lower than hydrogen's LEL or is less than 4% (orless than 40000 ppm) of H₂ in air. The required flow rate of the diluentair can be calculated from the amount of current used during electrolytegeneration, which is correlated with the rate of hydrogen generation atthe cathode. For example, if the reactor current is I Amperes, theexpected volumetric rate (R) of hydrogen generation in liters per minutewill be:

R=22.4×I×60/(n×F),

where 22.4 L is a volume of one mole of gas at a standard temperatureand pressure (at 1 atmosphere and 20 degrees C.), 60 is the number ofseconds in a minute, n is the number of electrons required per mole ofhydrogen product produced (2 electrons), and F is a Faraday's constant(96500 coulombs per mole of electrons). For a system running at 100Amps, the rate of hydrogen gas generation calculated according to thisformula will be about 0.007 liters per minute. If an air diluent streamwith a volume flow rate of (0.007×4)/0.04=0.7 lpm is introduced intomanifold 693, the concentration of hydrogen will, on average be ¼ theLEL level in that chamber. In one of preferred embodiments and in orderto increase the safety of the operation, an inert gas (e.g. nitrogen orargon) is used as the diluent gas instead of air. In this case, there isessentially no oxygen in the chamber, and the mixture exiting thechamber is at a dilution level that is far below the required dilutionif the diluent were air. In this case any subsequent dilutions with airwill always lead to decreasing hydrogen concentration below the LEL.This configuration significantly minimizes fire and explosion risks bothin the cathode-housing assembly and elsewhere in the electrolytegenerator.

In some embodiments, an optional feature 697 is provided on thecathode-facing side of the inner lid 675, where the feature acts as asplatter flow separation guard. As bubbles of hydrogen break while theyrise from the gap 687, droplets of catholyte may be splattered onto theinner lid 675 and can accumulate on the inner portion of the lid underthe influence of surface tension forces, particularly right above thegap. In one of the embodiments the inner lid 675 is positioned at anangle to the horizontal plane, preferably at an angle of between about5-20 degrees. The slope of lid 675 allows the accumulated catholytedroplets to move by gravitational force in the general direction of theinner lid outlet holes 699. The splatter flow separation guard 697 ispositioned to prevent the droplets from flying through the holes, orfrom flowing along the surface of the inner lid and being drawn up ontothe opposite (top) surface of the inner lid 675. The splatter guard 697also redirects the flow of the splattered catholyte on the bottomsurface of the inner lid 675 downwards and back into the catholytebelow. This prevents the splattered catholyte from being potentiallydrawn up by the gas flow out of the catholyte chamber.

The fluid levels in the anolyte chamber and in the second catholytechamber are actively monitored in the depicted apparatus for reliabilityproblems (such as for low level of electrolyte and for overflow ofelectrolyte). The monitoring is performed by fluid level sensors thatare in communication with an apparatus controller. One example of aparticularly useful low cost level sensor is the combination of apressure transducer (available, for example, from Dwyer of Wilmington,N.C.) teed into a line and connected to a gas bubbling line 701, wherethe sensed pressure is correlated to the fluid surface level above theend of the bubbling line tube opening “h”, by the following expression:

ΔP=Σgh.

If an inert gas (e.g., nitrogen or argon) is used for bubbling in thistype of sensor, such bubbling sensor would have the additional benefitof serving as a deoxygenation device for the fluid that is beingmeasured (e.g., anolyte or catholyte). Therefore, in some embodiments aninert gas is supplied from an inert gas source to the sensor and isbubbled through the fluid. Another example of a continuous levelmonitoring sensor is an ultrasonic reflection depth sensor. These andsimilar functional sensors can continuously measure the actual level offluid (e.g., anolyte and catholyte), in contrast to trip level typesensors, which send a unique signal when the level of fluid is eitherabove or below a target level setting. It is understood, that trip leveltype sensors can be used in some embodiments in the provided apparatus.Examples of target (trip) level sensors include capacitive level sensorsand float switches.

In one of the preferred embodiments, the electrolyte-generatingapparatus includes a densitometer and a conductivity meter configured tomeasure both the density and conductivity of the anolyte. Thecombination of density and conductivity is correlated to compositionaldata of the anolyte to simultaneously determine and control the metaland acid content in the anolyte. An inline densitometer, such as an inline MEMS based densitometer unit produced by Integrated Sensing Systemsof Ypsilanti, Mich., can measure the fluid density of the anolyte withan accuracy of 0.0005 g/cm³. In one embodiment, the target density ofthe tin anolyte, when it reaches the desired concentration of tin ionsand becomes the product electrolyte is about 1.50 g/cm³. The density ofmetal-containing product electrolyte typically has a stronger dependenceon metal ion content than on acid content, due to the larger partialmolar density of metal ions. A family of data curves of conductivity anddensity as a function of metal ion content (at different fixed acidconcentrations) can be obtained and used to determine the compositionalunknown quantities (e.g., metal ion and/or acid concentrations)continuously and accurately. Thus, monitoring of density andconductivity is useful for determining two compositional concentrations(e.g. acid and metal content), and allows for process adjustments suchas addition of acid, water, or provision of additional charge forgeneration of additional metal ions. A similar process can be used ifusing different measured intrinsic property measurements pairs. Theminimum number of measurements is equal to the number of materials(ionic pairs) being measured (two for a two component system with asingle anion, or three for three components with three components and asingle anion). Examples of intrinsic properties that could beused/measured in combination include density, viscosity, osmoticpressure, conductivity, refractive index, pH, and optical absorbance ata given frequency. As some of these intrinsic variables can have strongtemperature dependency (density and optical absorbance of a fluid beingnotable exceptions) it is also important to measure the temperature andrecord change in property response with temperature if temperature isnot fixed during the measurement, and to know the differential change inthe response with temperature. Many sensors include build in thermalcouples or thermistors.

The passage of current through the resistive electrolyte in the reactorgenerates heat. In some embodiments, a heat exchanger is provided ineither the anolyte chamber, the catholyte chamber, or both. In thedepicted example, the heat exchanger is provided only in the coolingsection 629 of the anolyte chamber 613. The illustrated heat exchangeris composed of a main titanium pipe inlet manifold 703, which feedsseveral (e.g., 4) weld-connected heat exchange titanium pipes 704 ofsmaller diameter that serpentine back and forth in the anolyte reactorcooling area. At the opposite end of the chamber, the smaller tubes 704connect to an exit port manifold 705. A cooling fluid, such as facilityliquid cooling water or a cooling fluid generated and circulated by anexternal chiller unit, circulates through the heat exchanger to cool theanolyte and maintain it at a target temperature (e.g., at less thanabout 40° C.). In one embodiment, the temperature of the anolyte iscontrolled by opening a liquid cooling water inlet valve when thetemperature of the electrolyte exceeds a target maximum temperature. Inother cases the temperature is actively controlled using the sensedtemperature and a feedback controller of an external fluidic chillerunit. An anolyte temperature sensor is provided for this purpose.

The depicted electrolyte-generating reactor further contains an overflowweir. A fluid entering the anode reaction region and passing upwardsthrough the porous anode particles flows upwards to an overflow porousregion or “weir”. After the flow reaches the weir, it changes directionand then flows through the anode containment plate assembly in ahorizontal direction. In one of embodiments, the apparatus includes afluid and particle diversion trough or “gutter” 709 that has a slopedcollection surface that is configured to collect and confine the fluidflowing out of the overflow weir and to direct it to a peripheral coarseparticle filtering assembly 711. This fluid will typically containparticles formed at the anode that should be removed by filtration. Thegutter 709 empties the fluid into a removable sock-type filter unit (notshown), which is configured to remove coarse particles from the fluid.The fluid enters into the open portion of the sock-type filter and afterfiltration the fluid exits the filter assembly 711 through openings inthe wall of the main anode chamber 713. The filter sock can be removedand cleaned or disposed of and replaced. The coarse particle filteringassembly 711 with accessible removable filter sock diverts recirculatedflow for separation of coarse particles in the product, reduces the loadon the fine filter assembly 639, and allows for the quick and easyremoval of the filter without draining the reactor or turning thereactor off. The gutter is illustrated primarily with reference to FIG.7C which presents a cross-sectional view of a portion of the apparatuswhere the plane of the cross-section is perpendicular to the plane ofthe cross-section used in FIG. 6C.

Electrolyte Generation Process

The metal electrolyte generation and control processes are illustratedin FIGS. 8A-8B, and 9A-9F. The processes are carried out in theelectrolyte generation systems described herein. In a batch process,illustrated in FIG. 8A, the process starts in 801 by passing currentthrough an apparatus having an active anode (e.g., low alpha tin anode)and a hydrogen-generating cathode separated by a membrane. The apparatus(anolyte and catholyte chambers) is originally charged with anelectrolyte (e.g., with an aqueous solution of an acid), and powersupply delivers sufficient current to the anode and the cathode to causethe dissolution of the anode. In one example, an initially empty anolytechamber having a tin anode is charged with a predetermined appropriateamount of acid (e.g., methanesulfonic acid and/or sulfuric acid) andwater, and the catholyte chamber (or chambers) is also charged with apredetermined amount of acid. In some embodiments, the concentration ofacid in the anolyte before current is applied is lower than theconcentration of acid in the catholyte. Furthermore, in one of thepreferred embodiments, the anolyte (before current is applied) containstin (II) salt in addition to the acid. For example, in one embodimentthe anolyte initially contains tin (II) methanesulfonate and MSA, whilecatholyte contains only MSA at a higher concentration than theconcentration of MSA in the anolyte. It was discovered that it ispreferable (although not necessary) to start the process by providingtin ions in the anolyte that would be at least about 60%, morepreferably at least about 80% of the tin target concentration, andparticularly preferable at least about 90% of the tin targetconcentration, and to start with an acid concentration in the anolyte ofless than 1 M, such as between about 0.3-0.7 M, e.g., 0.5-0.7 M. Forexample, in some embodiments it is preferable to provide a concentrationof tin ions in the anolyte (before application of current) of at leastabout 200 g/L, such as at least about 250 g/L. Providing tin ions in theanolyte before application of current provides the advantage of improvedanolyte and system stability. Specifically, it was discovered thatsolutions containing low concentrations of tin ions (and secondly highconcentrations of acid) are relatively less stable than solutions withhigher tin ion concentrations (and low acid). By providing a relativelyhigh concentration of tin ions before current is applied, it is ensuredthat the concentration of tin ions will only increase after the currentis applied and the anolyte will remain highly stable. The formation ofundesirable Sn⁴⁺ ions and associated particle generation is generallysuppressed under these preferred operating anolyte concentrations.Furthermore, if no tin ions are in the anolyte before application ofcurrent, the concentration of tin ions will increase from zero to atarget concentration (e.g., to 300 g/L), which may cause undesiredosmotic effects and can impact the membrane more than a more modestincrease in tin ion concentration (e.g., from 250 g/L to 300 g/L). Themaintenance of a relatively low concentration of acid (e.g., 0.3-1Mconcentration) in the anolyte also confers higher stability to theanolyte.

Referring again to FIG. 8A, in operation 801, current is supplied to thereactor to cause dissolution of metallic (e.g., low alpha tin) anode.The current is supplied such that the total charge delivered to thesystem is sufficient to generate the target concentration range of tinions in the anolyte. For example if the broad target concentration rangefor tin ions is between about 280-320 g/L, the current is supplied foran amount of time that is necessary to generate the required amount oftin ions in the anolyte and to reach the target concentration in a knownvolume of the anolyte. The time is calculated based on Faraday's law ofelectrolysis, given that the level of supplied current and the volume ofthe anolyte are known parameters. The apparatus typically includes atimer interfacing with the apparatus controller, where the controllerprovides instructions for starting and stopping application of currentbased on the input from the timer. In one example, the charge requiredto generate 456 g of tin ions in the anolyte is about 206 A·h. In thisexample, current can be applied at a level of 100 A for about 124minutes. The level of current provided to the apparatus can vary andwill generally depend on the circulation flow rate in the reactor, andon the projected area of the anode pellets to the counter electrode.

The concentration of metal ions in the anolyte is measured in operation803. For example, the concentration of tin ions can be measured usingdensitometry, either alone or in combination with the measurement ofconductivity of the anolyte. The concentration can be measuredcontinuously before, during, and after application of current, orintermittently. In some embodiments, the concentration of metal ions ismeasured shortly after application of current is stopped. After thetarget concentration of metal is reached, and it is confirmed by themetal concentration sensor, the anolyte is transferred in an operation805 to the electrolyte storage container. Optionally, the concentrationof acid in the anolyte is also measured and may be adjusted before theanolyte is transferred to the electrolyte storage container. Theconcentration of acid can be measured using a conductivity sensormeasuring the conductivity of the anolyte (provided that theconcentration of metal ions is known). After the target concentration ofmetal ions is reached in the anolyte, the residual acid concentration atthat point may be at a target level, too high or too low. If theconcentration of acid is at the target level, the batch process iscompleted, and the anolyte (all of it or only a portion of it) istransferred to the electrolyte storage container in the operation 805.If the concentration of acid is low, additional acid is transferred tothe anolyte in the amount that is necessary to reach the target level ofacid. If that dilution due to the acid addition is sufficiently small tonot drive the metal ion concentration below the lower control targetlimit (below the broad metal ion target concentration range), the batchgeneration cycle is complete, and the anolyte is transferred to theelectrolyte storage container. If the amount of added acid does dilutethe anolyte such that the metal ion concentration is below the targetmetal ion concentration range, additional charge is applied to thesystem to bring the metal ion concentration into the broad range fortarget concentration. The adjustment process (addition of acid toanolyte, and passing of additional charge through the system) can berepeated, and can also include removal of a portion of anolyte from thereactor to waste, if needed, until the target concentrations of metalions and of acid are achieved. If the acid concentration is too high,one method of recovery is to remove a portion of the anolyte to waste,replace some or all of that removed volume with water, and generateadditional metal ions by passing additional current through theapparatus until both the metal and acid concentrations are inside thebroad target concentration control limits. In subsequent cycles,information related to the corrective actions for this cycle is used tomodify the initial amount of acid/water and charge for the cycle. Therole of the metal ion concentration sensor may be monitoring of metalion concentration in the electrolyte to prevent transfer of electrolyteto the storage container, if the concentration of metal ions is notwithin the broad target range, collection of data for adjustment ofprocess parameters in subsequent batches during electrolyte generationif the concentration of metal ions is within the broad target range butis outside the narrow target range. Additionally, in some embodimentsthe metal concentration sensor will directly signal the controller tostop the application of current after target concentration range ofmetal ions (e.g., target density range) is reached. In this embodimentthe sensor can be used instead of the timer to provide the “current-off”signal.

In some embodiments the electrolyte generation process is performedcontinuously using a plurality of cycles, wherein each cycle generates abatch of electrolyte. The process flow diagram shown in FIG. 8Billustrates a cyclic process for electrolyte generation, where eachcycle involves removal of only a portion of generated electrolyteproduct to the electrolyte storage container. The process starts in 809,similarly to the process shown in FIG. 8A, by passing current through anapparatus having an active metal anode and an inert hydrogen generatingcathode, and monitoring concentration of metal ions in operation 811.Next, after a target concentration of metal ions is reached in theanolyte, only a portion of the anolyte (electrolyte product) is removedto the electrolyte storage container in operation 813. In one of thepreferred embodiments, the removed portion is relatively small and ispreferably less than about 20%, such as less than about 15%, such asbetween about 1-10% (e.g., about 5%) of the total volume of the anolyte.Next, in operation 815, the anolyte chamber is replenished with acid. Inthis step, an appropriate amount of acid and water is added to theanolyte. Next, current is delivered to the electrolytic cell again,until the concentration of the anolyte returns to the broad targetcontrol range, and a portion of electrolyte is again removed to thestorage container. Thus, as shown in operation 817, the steps 809-813are repeated. In some embodiments, each cycle further includes adding anecessary amount of acid to the catholyte.

Transfer of small amounts of electrolyte product to the storage in asingle cycle has a number of advantages over transfer of the entireanolyte, and over transfer of large amount of anolyte. When smallamounts of electrolyte product are transferred to storage, theperturbation from the target concentration of both acid and metal ion issmall over the course of each cycle, because the amount of dilution atthe beginning of the cycle is small (e.g. 5%), and because the change inionic strength and therefore osmotic pressure of the anolyte relative tothe catholyte over the cycle is small. The process can be designed suchthat osmotic pressure on the catholyte side is nearly identical to thepressure on the anolyte side, and water transport due to osmosis can beminimized. While electro-osmotic drag, which tends to transfer waterwith the moving ions (in this case with the anions moving through theanionic membrane) can be significant, it is measureable, calculable andrepeatable for each of the process sequences. Therefore, the amount ofwater lost by the anolyte due to electro-osmotic drag in each cycle isknown, and the lost water can be easily replaced. Therefore, in someembodiments the process is conducted such that the concentration of Sn²⁺in the anolyte does not fluctuate by more than 10%, such as by more than3% over the course of several generation cycles (e.g., 5 generationcycles). Also, preferably the concentration of acid in the anolyte doesnot fluctuate by more than 100%, such as by more than 50% over thecourse of several generation cycles (e.g., 5 generation cycles).

Another advantage of removing only a small amount of electrolyte pereach cycle is that the concentration of metal ions can be maintainedthroughout the cycles at a relatively high level. It was observed thatan electrolyte having high concentration of Sn²⁺ ions andmethanesulfonate as a counter ion is much more resistive to oxidation toSn⁴⁺ species than an electrolyte having a low concentration of Sn²⁺.Therefore, in some embodiments, the concentration of Sn²⁺ ions ismaintained at least at 250 g/L, more preferably at least at 270 g/Lduring one cycle or during a plurality of cycles. In some embodimentsthe concentration of tin ions at the beginning of each cycle is at leastabout 90% of the target tion ion concentration. In one example, theconcentration of tin ions is about 95% of the target tin ionconcentration. For example at the beginning of the cycle concentrationof tin ions may be 285 g/L, and after generation is complete the anolytereaches a target tin ion concentration of 300 g/L. Maintaining a highanolyte tin concentration throughout the process has significantadvantages related to the purity of obtained electrolyte and efficiencyof the process.

When cyclic process is used, the current can be applied to the generatorelectrodes continuously or intermittently. In one of the embodiments,when current is applied to the electrodes, no acid or water is added tothe apparatus, and the electrolyte product is not transferred to thestorage tank. This embodiment is advantageous because it is easier tomaintain the balanced concentrations of components and to orchestratetransfers of fluids, since concentration of metal ions in the anolyte isconstant when current is not applied. In other embodiments, acid may beadded to the anolyte without turning off the current. The advantage ofthis embodiment is that small amounts of acid can be added to theanolyte with high frequency, thereby minimizing acid concentrationfluctuations in the anolyte and minimizing related osmotic effects.Finally, in other embodiments application of current may be continuousand is not stopped when electrolyte product is transferred to thestorage container, and when the anolyte and catholyte are dosed withacid and water. The advantage of this embodiment is its high efficiency.

It is understood that the methods illustrated in FIGS. 8A and 8B canfurther incorporate any of the steps that were previously discussed inconjunction with the description of the apparatus. Thus, the methods mayinvolve providing one or more diluent gases to the electrolytegenerating apparatus in order to dilute generated hydrogen gas andremove the diluted gas through an exhaust. The methods may furtherinclude deoxygenating anolyte and/or catholyte by, for example, bubblingan inert gas. Furthermore, the methods may involve periodically removingthe second catholyte (e.g., a portion of the second catholyte) from thesecond catholyte chamber and filling the second catholyte chamber with afresh acidic solution.

One of the important features of an automated multi-cycle electrolytegeneration process, is the maintenance of stable concentrations ofanolyte and catholyte components and maintenance of mass balance forthese components throughout the cycles. Maintaining mass balanceinvolves adding defined amounts of acid and water to anolyte andcatholyte to accurately compensate for consumed and transferred acid andwater in the anolyte and catholyte chambers. For example, in a cyclicprocess that involves application of current to the electrodes togenerate tin ions in the anolyte, followed by transfer of a portion ofanolyte product from the anolyte to the storage tank, and followed byaddition of acid solution (and optionally water) to the anolyte andcatholyte, the amounts of added water and acid are calculated such thatthe amount of tin ions and acid in the anolyte, and the amount of acidin the catholyte before application of current is substantially the sameas the corresponding amounts of tin and acid at the end of the cycle(after current has been applied, a portion of electrolyte has beentransferred, and acid and/or water have been added to the anolyte andcatholyte chambers). More preferably, not only the amounts of tin ionsand acid are substantially the same, but also the concentrations of tinions and acid are substantially the same.

The amounts of acid and water that need to be added to anolyte andcatholyte to maintain mass and concentration balance over a plurality ofcycles, can be calculated and programmed into a system controller. Forexample, in one of the embodiments employing tin ions, methanesulphonate(MS) ions, and MSA, and an anion-permeable membrane, the amounts of acidand water are calculated based on the facts that during application of adefined amount of charge, a known amount of MSA moves from the anolytechamber to the catholyte chamber, and a known amount of MS moves in theopposite direction from the catholyte chamber to the anolyte chamberalong with some amount of water. Furthermore, the calculation takes intoaccount the known amount of tin that is generated during application ofcharge in the anolyte, the known amount of acid that is lost from thecatholyte during application of charge to generate hydrogen gas, and theamounts of acid and tin that are removed during transfer to the productstorage tank.

Three examples of maintaining mass balance in three different cyclicprocesses are illustrated in FIGS. 9A-9F. These schemes show theconcentrations and amounts of components in the anolyte and catholyte atdifferent stages of the process. FIGS. 9A-9B illustrate a cycle in whichno material transfer is occurring when current is applied to theelectrodes, and where catholyte (first catholyte chamber) serves as thesource of acid for the anolyte (a cascade embodiment). The depictedprocess starts in 901, where the electrolyte at a target tin ionconcentration of 304 g/L has been generated in the anolyte. When theelectrolyte is generated, the concentrations of tin ions and of acid inthe anolyte are measured by the conductivity and density sensors. If theconcentrations of tin ions and acid are too high at the end ofgeneration, water is added to the anolyte to bring the concentrations tothe target. If the concentration of tin is too low, additional charge ispassed through the system to reach the target concentration. If theconcentration of acid is insufficient, then acid is added to theanolyte. If both concentrations of tin ions and of acid are at a broadtarget level, 5% of the total anolyte volume (1.5 L of 30 L anolyte) istransferred to an electrolyte storage container, as shown in FIG. 9A.Next, in 903, after a portion of the anolyte has been removed tostorage, the volume of the anolyte is low and is at 28.5 L. Theconductivity of the anolyte is checked, and, if it is too high, morewater is added to the anolyte. If the conductivity is too low, then moreacid is added. If the conductivity is at the broad target level, 1.17 Lof catholyte (acid) is transferred to the anolyte. The 1.17 L ofcatholyte are used to make up for 0.165 L of acid transferred from theanolyte to the storage container with the product electrolyte and for1.005 L of acid that migrated from the anolyte to catholyte through themembrane during tin ion generation. This results in composition 905, inwhich the anolyte has the required amount of acid. Next, water is addedto the anolyte until the original anolyte volume (30 L) is reached,resulting in composition 907, in which the anolyte is ready forapplication of current. In the next step, acid needs to be added to thecatholyte to make up for the acid transferred to the anolyte and removedwith the electrolyte to storage (0.072 L) and for the acid that will beused to make hydrogen gas in the following run (0.781 L). Therefore,0.853 L of 70% MSA are dosed to the catholyte from the acid toteresulting in composition 909. Finally, deionized water is added to thecatholyte to top it off to 30 L resulting in composition 911, in whichboth the anolyte and the catholyte are ready for generation ofelectrolyte. Next, power is applied to the anode and the cathode and apre-calculated amount of charge (205.9 Ah) is passed through the systemto generate more tin ions in the anolyte. While power is applied, 416. 9g of MSA are transferred from the anolyte to catholyte, and 730.8 g ofmethanesulfonate are transferred from the catholyte to the anolytethrough the membrane. Also, during the course of electrolyte generation456 g of tin ions are formed in the anolyte from the anode, and 7.7 g ofhydrogen are removed from the catholyte. The resulting compositions ofthe anolyte and catholyte 913 at the end of application of current arethe same as after previous application of current 901. In sum, 806.8 gof MSA are added to the electrolyte generator from the acid tote, and456 g of tin ions are added to the solution from the anode, resulting in1262.8 g of total added materials, whereas 1255.2 g of productelectrolyte is removed to storage and 7.7 g of hydrogen is removed fromthe apparatus, resulting in 1262.9 g of removed materials, therebysubstantially completing the mass balance.

While in the embodiment illustrated by FIGS. 9A and 9B, addition of acidand water to the anolyte is performed while the power is not provided tothe electrodes, in other embodiments it is possible to add acid to theapparatus while generating electrolyte (while applying power to theelectrodes). This embodiment is illustrated with reference to FIGS. 9Cand 9D. The steps 921-923 of this method are similar to the stepsillustrated in FIGS. 9A and 9B, while the amount of acid dosed toanolyte and catholyte is scaled down to reflect than only 10% of theamount of charge that was applied in the method illustrated in FIGS. 9Aand 9B. Thus, while charge is being applied (at the 10% level), acid isbeing dosed to anolyte and catholyte (at the appropriate levelcorresponding to 10%). This intermittent acid dosing can be performedfor example 10 times while more charge is applied. This method isreferred to as the segmented acid method to indicate that unlike in thepreviously illustrated method, where the acid was added to the anolyteand catholyte at 100% when current was applied, in this method the acidis divided into ten segments that are added at regular intervals whilecurrent is being applied to the electrodes of the apparatus. Transfer ofthe product to the storage tank can be performed after current isstopped.

In some embodiments it may be more preferable to remove portions ofcatholyte from the first catholyte chamber to drain, instead oftransferring them to the anolyte chamber as was illustrated in FIGS.9A-9D. In these embodiments, the first catholyte chamber does not serveas a source of acid for the anolyte. Instead acid is added to both theanolyte and catholyte from a source of acid, such as an acid storagetank. Removal of portions of catholyte from the first catholyte chamberto the drain may be useful, because catholyte in the first catholytechamber may be contaminated with Sn⁴⁺ ions, and it may be moreeconomically feasible to remove these portions from the system. Anexample of a process scheme illustrating mass balance maintenance forsuch embodiment is shown in FIGS. 9E and 9F. Referring to FIG. 9E theprocess starts in 941, after a pre-determined amount of charge haspassed through the generator, indicating that the anolyte has sufficientconcentration and is ready to be transferred to the storage tank. Atthis point, density and conductivity of the anolyte are checked, and ifboth are within the broad target range, it is determined that theanolyte can be transferred. In the depicted example, in 941 (before thetransfer), the anolyte chamber contains 30 liters of an aqueous solutioncontaining Sn²⁺ ions (9120 g), methanesulfonate ions (14615 g), andmethanesulfonic acid (1368 g). The catholyte (including first and secondcatholytes) is 29.4 L of an aqueous solution containing methanesulfonicacid (12445 g). It is noted that in this illustration the catholyte haslost about 0.6 L of volume to the anolyte during previous cycle, becausewater was transferred through the membrane from the catholyte to theanolyte together with the methanesulfonate ions when current was appliedto the cell in the previous cycle. After current was stopped, 5% of thetotal anolyte volume is transferred to the storage tank, leaving anolytewith low volume as shown in 943. In the next step, conductivity of thecatholyte is checked, and if the conductivity is within a broad targetrange, a portion of catholyte from the first catholyte chamber isremoved to drain. As shown in 945, 0.1 L of catholyte containing 42.3 gof methanesulfonic acid is removed from the first catholyte chamber,leaving 29.3 L of total catholyte volume and 12403 g of the MSA in thecatholyte (including catholyte in the first and second catholytechambers that fluidically communicate through a conduit other than amembrane). The next step is to replenish the anolyte, such that a massbalance is maintained. In this step, the anolyte is dosed with the acid,such that the amount of added acid is substantially equal to the sum ofamount of acid removed from the anolyte to the electrolyte storage tank(68.4 g of MSA) and the amount of acid that will be transferred from theanolyte to the catholyte through the membrane, when current will beapplied (416.9 g). The latter amount is known for a specific type ofmembrane that is used, based on the known amount of charge that is beingpassed through the electrolyte generator during one run. Accordingly, anaqueous solution of MSA containing about 485 g of MSA is added to theanolyte from an acid tank. The anolyte is further topped off with water(0.37 L), until its volume reaches 29.38 L. The amount of water that isadded in this step, is determined such as to bring the volume of theanolyte to the desired target (in this illustration 30 liters) afterwater will be transferred from the catholyte to the anolyte duringapplication of current to the cell. After acid and water were added tothe anolyte, the anolyte is ready for electrolyte generation, as shownin 947. Next, catholyte is replenished with the acid. In this step 363.7g of MSA is added to the second catholyte chamber from the MSA solutiontank. This amount of added acid is substantially equal to the amount ofMSA that will be lost from the catholyte during this cycle to generateH₂, plus the amount of MSA that was transferred to the drain from thefirst catholyte chamber in 945 flush, minus the amount of MSA that willmigrate from the catholyte to the anolyte during this cycle when currentwill be applied. The composition of the resulting catholyte is shown in949. Next, the catholyte is topped off with 0.32 L of water to bring thecatholyte volume to 30 L. At this point the catholyte is ready as shownin 951. Next, a pre-determined amount of charge (205.9 A·h) is passedthrough the cell, resulting in generation of 456 g of Sn²⁺ ions in theanolyte, and removal of 7.7 g of H₂ at the cathode. Also, duringapplication of current to the electrodes, 416.9 g of MSA is transferredfrom the anolyte to the catholyte through the membrane, and 730.8 g ofmethanesulfonate along with 0.62 L of water is transferred from thecatholyte to the anolyte across the membrane. After the pre-determinedamount of charge has been passed, the cycle is completed and the anolyteand catholyte compositions in 953 are substantially the same as theywere at the start of the cycle in 941. In total the mass of MSA and tinions that enter the generator in one cycle is equal to the mass of H₂,MSA, and tin ions that exit the generator in the cycle (to the exhaust,to the product storage and to the drain). In the depicted example 1305.2g of materials entered and exited the system as described.

One of the prominent features of the provided electrolyte generatingapparatus is its ability to provide feedback on electrolyte compositionusing one or more sensors, such as an anolyte density meter, anolyteconductivity meter, a catholyte conductivity meter, or a combinationthereof In some embodiments the sensors are used in order to adjustelectrolyte generation process parameters, if an unacceptable drift inelectrolyte composition is detected. The sensors are also used to signalthat the process needs to be shut down, if one or more electrolyteproperties fall outside a broad desired range. For example, if anolytedensity, measured by the densitometer falls outside the broad targetrange, it indicates that the concentration of tin ions in the anolyte isnot acceptable, and that the generated tin electrolyte should not betransferred to the product tank. On the other hand, if anolyte densityfalls inside the broad target range but outside the narrow target range,this would indicate that the anolyte still has an acceptableconcentration of tin ions and can be transferred to the product storagetank, but that process parameters for subsequent generation cyclesshould be adjusted such that the density is restored to the narrowtarget range, and the drift in density is eliminated.

FIG. 10 provides an illustration for a method of adjusting electrolytegeneration process parameters based on the anolyte density reading. FIG.10 shows anolyte density values as a function of cycle number. In eachcycle the plotted density is measured after current is stopped andbefore the concentrations of anolyte and catholyte are adjusted. In thedepicted example the density range of 1.480-1.520 g/cm³ is the broadtarget density range, and the density range of 1.490-1.510 g/cm³ is thenarrow target density range. It can be seen that in the first elevencycles, the anolyte density falls both within the narrow and broadtarget ranges, and no adjustment is needed. At the 12^(th) cycle themeasured density of anolyte is 1.511 g/cm³ which falls outside thenarrow target range, but is still inside the broad target range.Therefore, the anolyte from the 12^(th) cycle is still transferred tothe product tank, but an adjustment of process parameters is triggeredby this density reading. It can be seen that the density drifted from1.500 to 1.511 g/cm³ over 12 cycles, corresponding to a 0.011 g/cm³positive drift. Such drift in density corresponds to 6.6 g/L excess oftin ion concentration. Since the volume of anolyte is about 30 liters inthis example, 6.6 g/L *30 L=198 g of excess tin ions is generated over12 cycles. Or, 198 g/12 cycles=16.5 g of excess tin ions are generatedin one cycle with the observed drift.

First, parameters in the next cycle 13 are adjusted to generate 198 g oftin ions less than in a normal cycle, and to thereby bring the densityof anolyte to the target level of 1.500 g/cm³. Assuming that onestandard cycle generates 450 g of tin ions, the 13^(th) cycle shouldgenerate 198 g less, or 252 g. In this cycle the current should beapplied for 252/450=0.56 of the time that was used in a regular run(assuming the same level of current is applied for all runs). In thenext step, the process parameters for all subsequent runs are adjustedbased on the observed drift of 16.5 g of tin per cycle. In order tocompensate for this drift, the duration of each subsequent run shouldbe: (450-16.5)/450=0.96 of the previous run time. Alternatively, theduration of the run may remain the same, but the level of current isreduced accordingly. More generally, the amount of charge that shouldpass through the system is adjusted by adjusting a duration of the run,the level of applied current, or both.

Drifts in anolyte conductivity and catholyte conductivity are addressedin a similar manner, but the adjustments are made not to the duration ofthe run, but to the amount of acid that is being added to anolyte andcatholyte during each cycle.

In some embodiments, the following rules are adhered to in order toprovide optimal process stability and to avoid overcorrections ofprocess parameters. First, it is preferable to adjust no more than oneproperty drift per cycle, even if several sensors indicate thatdifferent electrolyte properties are outside of the narrow target rangebut within the broad target range. For example, if in one cycle anolytedensity, anolyte conductivity, and catholyte conductivity are alloutside of the narrow target range (but within the broad target range),an adjustment of parameters in this cycle is made only to address thedrift in anolyte density, but not the drifts in anolyte and catholyteconductivities. If the anolyte density is within the narrow targetrange, but both anolyte and catholyte conductivities are outside of thenarrow target range, only the drift in anolyte conductivity is addressedin one cycle. Thus, the adjustment of parameters to address the drift inanolyte density is performed before addressing the drifts in anolyteconductivity and/or catholyte conductivity. An adjustment of parametersto address the drift in anolyte conductivity is performed beforeaddressing the drift in catholyte conductivity, and adjustments are madesuch that only one drift correction is made per cycle. Further, it ispreferable not to make frequent corrections to one type of parameter.For example, if sensors indicate that one parameter (e.g., anolytedensity) needs to be corrected more often than once in three cycles(i.e., if the parameter falls outside the narrow target range more oftenthan once in three cycles), the automated correction of parameter is notmade, and the problem is addressed by an engineer. Lower priorityparameters (anolyte and catholyte conductivities) are allowed to run outof narrow target range (but not out of broad target range) to allow 3cycles after a higher priority parameter adjustment. In the depictedexample, the priority of anolyte density is higher than the priority ofanolyte conductivity, which is in turn higher than the priority ofcatholyte conductivity. Finally, if any of the sensors indicate that anelectrolyte property (anolyte density, anolyte conductivity, orcatholyte conductivity) falls outside the broad target limit, theprocess is shut down, and the problem is addressed by an engineer.

In one embodiment of tin electrolyte generation, the broad target rangefor anolyte density is between about 1.4812-1.5296 g/cc; the broadtarget range for anolyte conductivity is between about 92-96 mS/cm; andthe broad target range for catholyte conductivity is between about451-491 mS/cm. In this illustrative embodiment, these parameters aremeasured after current is stopped being applied to the cell, and beforeaddition of acid to anolyte (for correction of anolyte conductivity) andcatholyte (for correction of catholyte conductivity).

FIGS. 11A-11D provide examples of algorithms for monitoring electrolyteproperties and adjusting process parameters in a tin electrolytegeneration process. In each cycle, after application of current isstopped, it is first determined if the anolyte density is within thenarrow target range, as shown in operation 1101 in FIG. 11A. If this istrue, it is then determined if the anolyte conductivity is within thenarrow target range, as shown in 1103. Next, if anolyte conductivity iswithin the narrow target range, catholyte conductivity is checked in1105. If catholyte conductivity is within the narrow target range, theprocess can proceed to the next run in 1107, which will includereplenishment of anolyte and catholyte with an acid and application ofcurrent in the next cycle. If, in operation 1101, it is determined thatthe anolyte density falls outside the narrow target range, the algorithmshown in FIG. 11B is followed. Referring to FIG. 11B, it is firstdetermined in 1201 if the anolyte density is within the broad targetrange. If anolyte density is outside the broad target range, this iscommunicated to the engineer in 1209. Typically, in this case theapparatus operator will receive an error message from the controller andthe apparatus will be configured not to proceed further. If anolytedensity is within the broad target range, then it is determined in 1203if there were more than three cycles since last density correction. Ifthere were three or less cycles since last density correction, then thedensity drifts too fast and this problem is communicated to an engineerin 1209, and the process is not allowed to proceed until the engineerresolves the fast drift issue. If there were more than three cyclessince last density correction, the process proceeds in 1205 bycalculating new constants for process parameters based on density drift,adjusting the density of the anolyte, and saving the newly calculatedconstants for the future run. The calculation can be performed as it wasshown with reference to FIG. 10. The newly calculated constants mayinclude the new duration of application of current or the new level ofcurrent. The adjustment of anolyte density can be performed by runningcurrent through the cell. If the density of the anolyte is too high, itcan be restored to a target value by running an additional short cycle(which includes removing a portion of anolyte to storage, dosing theanolyte with an acid, and running current for an amount of time that isnecessary to bring density to the target value). If the density is toolow, the anolyte is dosed with acid, the current is turned on, and tinion generation proceeds for an amount of time that is necessary to bringthe density to a target value. After the new process constants (e.g.,level of current to be applied and/or duration of current application)are saved, the counter that monitors the number of cycles since lastdensity correction is reset, and the process proceeds to the next run in1207.

Referring to FIG. 11A, if in 1103 the conductivity of the anolyte isoutside the narrow target range, then the algorithm shown in FIG. 11Cshould be followed. First, it is determined in 1301 if the anolyteconductivity is within the broad target range. If it is outside thebroad target range, this is communicated to an engineer in 1309, and theprocess is not allowed to proceed. Next, it is determined in 1303 ifthere were more than three cycles since last anolyte conductivitycorrection. If there were three cycles or less, the engineer is notifiedin 1309. The process is not allowed to proceed and the engineeraddresses the problem of excessively fast anolyte conductivity drift. Ifthere were more than three cycles since last anolyte conductivitycorrection, it is determined in 1305 if there were more than threecycles since last anolyte density correction. If there were three orless cycles since last anolyte density correction, then no correction toanolyte conductivity is made in this cycle and the next run is startedin 1311, while preserving the old constants. If there were more thanthree cycles since last anolyte density correction, then in 1307 newconstants are calculated based on anolyte conductivity drift, theconductivity of the anolyte is restored to the target value, and the newconstants are saved for use in subsequent cycles. If the density andconductivity data both indicate that the tin ion concentration is withinthe narrow target range, but the acid anolyte concentration is outsidethe narrow target range, the amount of acid that is to be added in agive cycle is adjusted (increased or decreased), such as to compensatefor the drift in the acid concentration. If the density of the anolyteis well controlled (e.g., within 1.48-1.52 g/cm³ range), then theanolyte conductivity value alone may be considered to determine if theamount of acid added in subsequent cycles should be adjusted, and thenew constants for the amounts of acid to-be-added are generated. Next, anew run is started in 1303 using the newly calculated process constants.

Referring to FIG. 11A, if in 1105 the conductivity of the catholyte isoutside the narrow target range, then the algorithm shown in FIG. 11Dshould be followed. First, it is determined in 1401 if the catholyteconductivity is within the broad target range. If it is outside thebroad target range, this is communicated to an engineer in 1409, and theprocess is shut down. Next, it is determined in 1403 if there were morethan three cycles since the last catholyte conductivity correction. Ifthere were three cycles or less, the engineer is notified in 1409. Theprocess is not allowed to proceed and the engineer addresses the problemof excessively fast catholyte conductivity drift. If there were morethan three cycles since last anolyte conductivity correction, it isdetermined in 1405 if there were more than three cycles since the lastanolyte conductivity correction. If there were three or less cyclessince the last anolyte conductivity correction, then no correction tocatholyte conductivity is made in this cycle and the next run is startedin 1411, while preserving the old constants. If there were more thanthree cycles since last anolyte conductivity correction, then in 1407new constants are calculated based on catholyte conductivity drift, theconductivity of the catholyte is restored to the target value, and thenew constants (amount of acid to be added to the catholyte) are savedfor use in subsequent cycles. When the drift in catholyte conductivityis observed than the amount of acid added to the catholyte in each cycle(after the conductivity is measured, and a portion of catholyte isremoved from the first catholyte chamber) is adjusted (increased if theconductivity is too high or decreased if the conductivity is too low),such that upon addition of water to the catholyte, the concentration ofacid would remain in the narrow target range. Next, a new run is startedin 1403 using the newly calculated process constants.

As it was previously mentioned the systems and apparatuses disclosedherein may include a process controller (or a plurality of controllers)having program instructions or built-in logic for performing any of themethods provided herein. Specifically the controller is configured toaccept information from one or more sensors, such as a densitometer, aconductivity meter, an electrolyte level sensor, to process theseparameters and to generate instructions for the apparatus, based on thedata acquired from a sensor or sensors. In addition one or severalcontrollers can be programmed to provide program instructions for anintegrated system including an electrolyte generator and one or moreelectroplating apparatuses, and may be configured to provide anelectrolyte having in desired amounts on demand.

In some implementations, a controller is part of a system, which may bepart of the above-described examples. Such systems can comprisesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller, in some implementations, may be a part of or coupled toa computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by comprising one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The apparatus/process described hereinabove may be used in conjunctionwith lithographic patterning tools or processes, for example, for thefabrication or manufacture of semiconductor devices, displays, LEDs,photovoltaic panels and the like. Typically, though not necessarily,such tools/processes will be used or conducted together in a commonfabrication facility. Lithographic patterning of a film typicallycomprises some or all of the following steps, each step enabled with anumber of possible tools: (1) application of photoresist on a workpiece,i.e., substrate, using a spin-on or spray-on tool; (2) curing ofphotoresist using a hot plate or furnace or UV curing tool; (3) exposingthe photoresist to visible or UV or x-ray light with a tool such as awafer stepper; (4) developing the resist so as to selectively removeresist and thereby pattern it using a tool such as a wet bench; (5)transferring the resist pattern into an underlying film or workpiece byusing a dry or plasma-assisted etching tool; and (6) removing the resistusing a tool such as an RF or microwave plasma resist stripper.

In one aspect, a non-transitory computer machine-readable mediumcomprising program instructions for control of an electrolyte generationand distribution tool is provided, wherein the program instructionscomprising code for performing any of the methods presented herein.

Experimental Density and Conductivity Measurements

In some embodiments both density and conductivity sensors are used todetermine when the metal and acid concentrations in the anolyte arewithin the target range. It was determined that the density of asolution containing Sn²⁺ salt depends linearly on the concentration ofSn²⁺ ions and exhibits relatively small changes with the variation ofacid concentration. FIG. 12A provides an experimental plot illustratingdependence of density of aqueous solutions containing tin (II)methanesulphonate, on the concentration of Sn²⁺ ions. FIG. 12A showsfour linear dependencies, where each linear function corresponds tosolutions having a constant concentration of methanesulfonic acid (0,30, 45, and 60 g/L). It can be seen that in all four cases a lineardependence on tin ion concentration is observed over a wide tin ionconcentration range (0-300 g/L of Sn²⁺) and that variations in densityof solutions having different acid concentrations, but same tin ionconcentration, are relatively small. FIG. 12B shows dependence ofsolution density on tin ion concentration for solutions containingmethanesulphonic acid at a concentration of 45 g/L and tin ions in arange of between 285 and 304 g/L. In some embodiments, theseconcentrations are the working ranges for the anolyte (i.e., theconcentration of MSA is about 45 g/L and the concentration of tin ionsis between about 285-305 g/L).

It was also shown that conductivity of solutions containing acid and atin salt linearly depends on the concentration of acid at a variety oftin ion concentrations. FIG. 12C shows a family of linear curvesillustrating the dependence of conductivity on the concentration of MSAin aqueous MSA solutions containing tin ions. The linear curve with thegreatest slope corresponds to MSA solutions containing no tin ions,while the linear curve with the smallest slope corresponds to MSAsolutions containing 304 g/L of tin ions. The remaining linear curvescorrespond to MSA solutions containing 50, 100, 150, 200, 250, and 300g/L of tin ions, where the slope of the linear curve decreases with theincreasing concentration of tin ions. FIG. 12D shows the linear curvescorresponding to MSA solutions containing tin ions at concentrations of350, 300, and 304 g/L for the MSA concentration range of between 30-60g/L. These concentrations, in some embodiments, are encountered asworking concentrations of MSA and tin ions in the anolyte duringelectrolyte generation. When the concentration of tin ions is stable,the conductivity alone can be used to determine the concentration ofacid in the anolyte, and to determine if adjustments to acidconcentration are needed.

1. An apparatus for generating an electrolyte containing metal ions, the apparatus comprising: (a) an anolyte chamber configured to contain an active anode and an anolyte, wherein the apparatus is configured to electrochemically dissolve the active anode into the anolyte, and to thereby form the electrolyte containing metal ions, wherein the anolyte chamber comprises: (i) an inlet for receiving a fluid; and (ii) an outlet for removing the anolyte; (b) a first catholyte chamber separated from the anolyte chamber by a first anion permeable membrane, wherein the first catholyte chamber is configured to contain a first catholyte, and wherein the first catholyte chamber comprises an inlet for receiving a fluid and an outlet for removing the first catholyte from the first catholyte chamber; (c) a second catholyte chamber configured to contain a cathode and a second catholyte, wherein the second catholyte chamber is separated from the first catholyte chamber by a second anion permeable membrane.
 2. The apparatus of claim 1, wherein the first catholyte chamber and the second catholyte chamber are parts of a removable cathode-housing assembly, wherein the removable cathode-housing assembly is configured to be releasably inserted into the anolyte chamber.
 3. The apparatus of claim 1, wherein the apparatus is configured to deliver the first catholyte from the first catholyte chamber to the anolyte chamber through a fluidic conduit connected to the outlet of the first catholyte chamber, and/or wherein the apparatus is configured to remove the first catholyte from the first catholyte chamber to a drain via the outlet of the first catholyte chamber.
 4. The apparatus of claim 1, further comprising one or more sensors configured for measuring a concentration of metal ions in the anolyte.
 5. The apparatus of claim 1, wherein the apparatus comprises a single piece metal anode.
 6. The apparatus of claim 1, wherein the anolyte chamber comprises an ion-permeable container for containing a plurality of metal pieces that serve as an anode.
 7. The apparatus of claim 6, wherein the anolyte chamber further comprises a receiving port for receiving a plurality of metal pieces into the ion-permeable container.
 8. The apparatus of claim 7, wherein the receiving port comprises a gravity fed hopper.
 9. The apparatus of claim 7, wherein the receiving port comprises a sensor configured to communicate to a system controller when the level of metal pieces in the receiving port is low.
 10. The apparatus of claim 1, wherein the apparatus comprises a hydrogen-generating cathode positioned in the second catholyte chamber.
 11. The apparatus of claim 10, wherein the apparatus comprises a diluent gas conduit configured to deliver a diluent gas to a space above the second catholyte, and to dilute hydrogen gas accumulating in that space, wherein the space above the second catholyte is covered with a first lid having one or more openings that allow for transfer of diluted hydrogen gas into a space above the first lid.
 12. The apparatus of claim 11, further comprising: a second lid over the first lid and spaced apart from the first lid such that there is a space between the first and the second lids; and a second diluent gas conduit configured to deliver a diluent gas to a space between the first and second lids and to move the diluted hydrogen gas from the space between the first and second lids towards an exhaust.
 13. The apparatus of claim 1, wherein the anolyte chamber comprises a cooling system.
 14. The apparatus of claim 1, wherein the anolyte chamber comprises a cooling system that is located in a cooling portion of the anolyte chamber away from the active anode.
 15. The apparatus of claim 14, further comprising a fluidic conduit and an associated pump configured to deliver the anolyte from the anolyte chamber outlet located proximate the active anode to the cooling portion of the anolyte chamber.
 16. The apparatus of claim 1, wherein the apparatus is configured to measure the concentration of metal ions in the anolyte with the one or more sensors, and to communicate the measurement to an apparatus controller.
 17. The apparatus of claim 16, wherein a single sensor is used for measuring the concentration of metal ions in the anolyte and the sensor is a densitometer.
 18. The apparatus of claim 16, wherein at least two sensors are used for measuring the concentration of metal ions in the anolyte, wherein the at least two sensors comprise a densitometer and a conductivity meter.
 19. The apparatus of claim 18, wherein the densitometer and the conductivity meter are further configured for measuring the concentration of acid in the anolyte.
 20. The apparatus of claim 19, wherein the conductivity meter is an inductive probe.
 21. The apparatus of claim 1, further comprising a sensor configured to measure a concentration of acid in the second catholyte.
 22. The apparatus of claim 1, wherein the apparatus comprises a controller having program instructions for automatically generating electrolyte having a concentration of metal ions in a target range.
 23. The apparatus of claim 1, further comprising a fluidic connection allowing for automated transfer of the anolyte from the anolyte chamber to an electrolyte storage tank, wherein the electrolyte storage tank is fluidically connected to an electroplating tool, and wherein the apparatus is configured to deliver the electrolyte from the electrolyte storage tank to the electroplating tool.
 24. The apparatus of claim 1, further comprising an accessible compartment configured for holding a replaceable source of an acid, wherein the replaceable source of an acid is fluidically connected with the inlet of the anolyte chamber, and said fluidic connection comprises an acid buffer tank, wherein the apparatus is configured to deliver the acid from the replaceable source of the acid to the acid buffer tank and from the acid buffer tank to the anolyte chamber.
 25. An apparatus for automatically generating an electrolyte containing metal ions, the apparatus comprising: (a) an anolyte chamber configured to contain an active anode and an anolyte, wherein the apparatus is configured to electrochemically dissolve the active anode into the anolyte, and to thereby form the electrolyte containing metal ions, wherein the anolyte chamber comprises: (i) an inlet for receiving a fluid; and (ii) an outlet for removing the anolyte; (b) a catholyte chamber configured to contain a cathode and a catholyte, wherein the catholyte chamber is separated from the anolyte chamber by an anion permeable membrane; (c) one or more sensors configured for measuring a concentration of metal ions in the anolyte; and (d) a controller having program instructions for causing an automatic generation of an electrolyte having a concentration of metal ions in the anolyte chamber in a target range using data provided by the one or more sensors, wherein the controller further comprises program instructions for causing a repeated transfer of a volume of anolyte from the anolyte chamber to a storage container, wherein the transferred volume of the anolyte in each transfer is no more than 20% of the total volume of the anolyte.
 26. A system comprising: (a) an electroplating apparatus that utilizes an electrolyte containing metal ions and an active soluble anode; (b) an electrolyte-generating apparatus configured for automatic generation of the electrolyte, wherein the electrolyte-generating apparatus is in communication with the electroplating apparatus; and (c) one or more system controllers comprising program instructions for communicating demand for electrolyte from the electroplating apparatus to the electrolyte-generating apparatus and for generating electrolyte having concentration of metal ions in a target range.
 27. A method of generating an electrolyte containing metal ions, the method comprising: (a) passing current through an electrolyte-generating apparatus, wherein the apparatus comprises: (i) an anolyte chamber cotaining an active metal anode and an anolyte; and (ii) a catholyte chamber containing a cathode and a catholyte, wherein the catholyte chamber is separated from the anolyte chamber by an anion-permeable membrane, wherein the anode is electrochemically dissolved into the anolyte as current is passed; (b) measuring concentration of metal ions in the anolyte, and automatically communicating the concentration to an apparatus controller, wherein the apparatus controller comprises program instructions for processing the data on concentration of metal ions and for automatically instructing the apparatus to act based on these data; and (c) automatically transferring a portion of the anolyte from the anolyte chamber to an electrolyte storage container, when concentration of metal ions in the anolyte falls within a target range, wherein the portion of the anolyte transferred to the electrolyte storage container is no more than 20% of the total anolyte volume. 